5.21pm: The Civil Aviation Authority have revealed what caused the outage. It is blaming an internal system network error at Airways New Zealand:
Airways immediately suspended all departing flights and operated as per its contingency planning procedures and enabled all flights to land safely using visual manual separation. The system was thoroughly tested and fully stable by 3.30 pm. Flights returned to partial operation by 4pm and then were fully operational at 4.30 pm. Flights were resumed on a priority basis with major trunk routes and jet flights resumed first.
Passengers can expect flights for the rest of the day.
Civil Aviation will investigate the cause or causes and work on a solution to prevent another outage.
"At no point were any passengers or aircraft at risk due to the implementation of Airways contingency planning procedures."
5.17pm: Delays have resulted in flight cancellations. Passengers at Christchurch Airport were told over the speakers that Air New Zealand flight NZ8832 from Christchurch to New Plymouth has been cancelled.
Flyers who checked in at Christchurch today have been asked to contact reservations. Those who have flown into Christchurch and are connecting on to New Plymouth are asked to collect their luggage and report to the check-in counter for overnight accommodation.
5.10pm: Tauranga couple Mike and Angela Newton, who are heading to Vancouver, are hoping their flight to Auckland will take off within the next hour. They need to be in Auckland in time to make their international which leaves at 8pm.
The couple, who were supposed to leave Tauranga Airport at 3.50, said they were not initially given any information besides and turned to the Air NZ app to find out what was going on. They were eventually called to the counter over the loudspeaker and told there were delays. At that stage they considered other options such as driving Auckland but their bags were already check.
"We have just decided to wait it out and see what happens. Hopefully we make it to Canada."
The latest information they have had is that their flight will hopefully leave at 5.30pm, which would get them to Auckland at 6pm and in time to make their international flight.
Mr Newton said he and his wife were off to Canada for the BC Bike Race, a 7-day mountain bike race around British Columbia. "We've been training for 9 months and dreaming of visiting Canada for many years longer. Hoping this is just a minor hiccup!"
5.00pm:Auckland Airport says there is no congestion in its terminals following the outage, which affected 20 domestic and five international flights.
Three of the grounded international flights had passengers on board.
He said the affected international flights had now all departed, but the backlog of domestic flights may take some time to clear.
Advice from Airways New Zealand was that the radar problem was partially fixed at 4pm and was completely operational again at 4.30pm
4.56pm: Transport Minister Simon Bridges has issued another statement:
I've been advised by the Civil Aviation Authority and Airways NZ that, following an internal network failure that resulted in the suspension of domestic flights this afternoon, services have now resumed. I have been assured that at no time was the safety of passengers or planes compromised.
4.53pm:More stories of passenger frustration from around New Zealand.
Reporter John Weekes in Wellington talked to Ben Heffey and Kate Synge, who had just arrived from the US and were already on a flight from Auckland to Wellington when they heard about the radar troubles. They said if their plane had left 30 minutes later, they'd have been stuck in Auckland.
They airport was packed when they arrived and the usual luggage carousel was unavailable. "All the flights from here south [were] cancelled as far as I know," Ms Synge said.
Jill Dixon and her grandson Jacob Ellery said their flight to Tauranga was cancelled this morning for reasons unexplained, then the radar glitch hit, delaying a second flight.
She and Jacob learned only a few minutes before boarding a 3.35pm flight that they'd have to stay put.
Ms Dixon, of Palmerston North, said Air New Zealand should put her and Jacob up for the night and pay her airport parking fees, which she estimated had ballooned an extra $45.
She parked at the airport because she had planned a quick return trip to the Bay of Plenty before returning home, but her plans were now in disarray.
4.43pm: NZME. News Service reporter Kurt Bayer has been talking to travellers at Christchurch International Airport. They are more philosophical than angry:
Dozens of travellers have had their travel plans thrown into disarray by the radar glitch. Snaking queues have formed at carriers' help desks as flyers try to find alternate journeys.
It's understood that international flights are getting priority.
Simon and Hilary Vallely, along with two-and-a-half year old Bree and baby Elsie left Rarotonga at 3.30am NZ time today. They were about to get on their third flight, from Christchurch to Dunedin, when their flight got cancelled. Now, they're trying to work out how to get home. "We might have to stay the night in Christchurch - these kids need to go to bed," he says.
While he was "frustrated" by the flight fiasco, he remained philosphical. "What can you do about it? I know they have to think safety but what about a bit of Kiwi she'll be right, kick in the guts kind of attitude?"
Geoff Neilson is equally calm about the delays to Dunedin. Instead of waiting for a new flight to be scheduled, he was going to rent a car and drive the four hours to Dunedin in order to make a business engagement tomorrow. He didn't want to risk Dunedin Airport being closed with frost. "We can hire a car and be well on the road but the time things are sorted here. There's nothing you can do about it."
4.43pm: The planes are moving again:
4.32pm:The problem that caused the grounding may be resolved but the backlog it has created has not. Air New Zealand says it will take some time to clear the backlog of delayed flights:
"Flights are now departing but the backlog will take some time to clear as approximately 160 international and domestic Air New Zealand flights have been impacted this afternoon and into this evening."
Flights to New Plymouth and Napier have been cancelled. Five others, to Hamilton, Rotorua, Nelson, Auckland and Invercargill were delayed. At least nine domestic flights to Wellington have been delayed but flights from Christchurch and Blenheim were expected to arrive on time.
4.29pm:From our reporter John Weekes in Wellington:
Queues are building at Wellington Airport as flyers wait to see when they'll be able to take off. Brisbane resident Anna Lane had planned to fly to Napier to visit her mum, who is recovering from a hip operation. She says she only just arrived in Wellington when she found out her next flight was cancelled.
As passengers strained to hear an airport PA announcement, it became clear international flights would take priority when the system got back up and running. Ms Lane says she was a patient person and expected to be delayed for hours. "There's nothing we can do so there's no use getting upset about it."
She says she'd hire a car and drive to Hawkes Bay rather than spend a night in Wellington.
4.24pm: Many passengers have complained that they were kept in the dark. Taki Bates told the Herald about the lack of information:
Whilst sitting at the gate waiting to board, I read an FB post from nzherald about radar problems. We are still waiting for any announcement. Have gone to ask desk staff and they have said that they are waiting for confirmation. They still haven't made any announcements and it's been 45 mins. Still waiting... no one knows what is happening.
Denise Cheese, from Auckland, says she is still sitting on a Christchurch flight at Auckland Airport, despite the problem being resolved. Her flight was meant to leave at 3.10pm. Passengers, including several with children, boarded at about 2.50pm but did not leave the gate.
"We were sitting there wondering why we hadn't taken off."
At about 3.30pm passengers, who were offered water by flight attendants, were told there was a problem.
Mrs Cheese says the pilot had been good at updating passengers since then. The latest update indicated plans should start taking off in five minute intervals but a couple of international flights would go first.
4.20pm: An NZME. News Service reporter at Christchurch Airport says he just saw a JetStar flight take off. A Jetstar spokesman said several hundred of the airline's passengers were affected over six flights. The longest delay for passengers is about 90-minutes, he says.
4.17pm:Auckland Airport says international flights will be operational again at 4.30pm, and domestic flights will be departing as soon as possible.
The network was told by Airways New Zealand that the whole network is now operational and flights will be departing.
During the radar outage, three planes were grounded at the international terminal and seven at the domestic terminal.
4.10pm: Whoops of delight across the country: the problem has now been RESOLVED. An Auckland Airport spokesman says Airways New Zealand has confirmed the fault was fixed and flights could now depart again.
4.07pm: A Civil Aviation Authority spokesman says the regulator is liaising with Airways New Zealand to ensure the problem is resolved as soon as possible.
4.05pm: This from a stranded passenger makes me think of the IT Crowd:
4.01pm: From the Minister of Transport, Simon Bridges:
I've been advised by the Civil Aviation Authority and Airways NZ that there has been an outage to the nationwide air radar network, the cause of which is not yet known. All departures have been suspended and the landing of any incoming aircraft is being staggered . Air traffic control is still able to communicate with any incoming planes via radio contact. I have been assured that there is absolutely no compromise to the safety of passengers of planes and I will be receiving regular updates.
3.54pm: Air New Zealand is not immediately able to comment on the volume of flights or passengers affected by the fault. The airline says staff are working to release more information soon.
3.49pm: From a passenger stuck on the tarmac:
Another one stuck in the departure lounge: "Sitting at Auckland International. No announcement about this... About to board so unsure as to what is happening."
- Taki Bates on Facebook writes.
3.49pm: Airways New Zealand spokeswoman Emily Davies says the cause of the radar failure remained unknown.
"We are aware of the failure that occurred at 2.48pm. We are currently working on the issue."
The fault has affected all flights in New Zealand at the moment, she said. The radar system was centrally controlled from Christchurch.
3.37pm: Christchurch Airport has said Airways is currently "experiencing an issue with its system across the country, which is resulting in a delay to departures from all the country's airports".
"The company is working to resolve the issue as quickly as possible," the airport said.
3.25pm: The fault means flights currently up in the air can land but no planes are allowed to take off.
An Auckland Airport spokesman told the Herald that all flights in the air could land, but departures were halted until the fault was resolved.
"We were informed by Airways New Zealand of a radar fault which is affecting all flights nationally," he said. "There is no resolution at this stage.
"All flights across the country are able to land but they are holding all departures until the fault is resolved."
A similar fault has occurred in previous years, he said.
