The Auckland Harbour Bridge has re-opened after it was closed earlier this morning because of strong wind gusts - but there are warnings it may be shut again if conditions demand.
Three lanes are now open in each direction, Auckland Transport says.
"Please expect significant delays and cancellations to services as the Auckland Harbour Bridge returns to normal and also note the bridge may close again on short notice."
The bridge was closed earlier this morning when wind gusts reached 98km/hr.
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Traffic was gridlocked in both directions approaching the bridge and crashes on the Northwestern and Southern motorways also caused delays across the city.
Just after 9am, Auckland Transport said double-decker buses were allowed back over the bridge, with services returning to normal routes depending on the weather.
Police earlier said that motorists could expect lengthy delays on alternative routes as well - with southbound traffic on the North Shore being diverted to the Upper Harbour Highway and northbound traffic from the Auckland CBD to the North Shore being diverted through SH16.
"We want people to delay travel and work from home if they can," they said.
Waka Kotahi NZTA said at 8.20am a serious crash just before 8am on the Northwestern, near Royal Road in Massey, West Auckland meant the road was briefly closed but one lane quickly re-opened.
A person was seriously injured in the collision, St John confirmed. The victim is in a serious condition and has been taken to Auckland City Hospital for treatment.
People heading north were told to expect long delays as a result and were being urged to take a different route or get off the Lincoln Road off-ramp.
About 9am, Waka Kotahi NZTA Auckland & Northland said that, following diversions due to the earlier bridge closure, and with lanes closed due to a crash on State Highway 16, travel north-south was best on State Highway 1.
They advised motorists to check travel times before departing to consider the best route.
By 9.40am, the crash had been cleared.
Another crash on the Northwestern Motorway was blocking the right lane citybound just prior to St Lukes Rd.
A crash on the Southern Motorway, after the Ellerslie Panmure Highway on-ramp, was also blocking a lane citybound.
Waka Kotahi NZ Transport Agency had said for several days that they were prepared to close the bridge if gusts reached more than 80km/h.
"A decision has been made to close all lanes on the harbour bridge to look after the safety of drivers and the bridge whilst the structure is still damaged and in a compromised state," NZTA said earlier this morning.
"Waka Kotahi acknowledges closing lanes on the bridge will cause major disruption and inconvenience, however safety is our top priority and the lanes closures will be lifted as soon as it is safe to do so."
NZTA said congestion was heavy and urged people to work from home where possible and avoid unnecessary travel.
"Check your route before you travel and use the Western Ring Route via SH16 and SH18 as an alternative to SH1 and the bridge."
Ongoing strong wind gusts have been a concern since the weekend and the bridge team has been continually measuring wind levels to assess whether the bridge has to close.
The New Zealand Herald's Sophie Ryan was on a bus approaching the harbour bridge this morning and said - after waiting for about half an hour - passengers were tense.
There were strong discussions held over whether to turn back or continue to wait.
"Ultimately the passengers asked to all turn around and the bus driver managed to turn around and onto the northbound side of the Northern Motorway."
She says he drove along to the Akoranga off-ramp and let them off the bus at the Akoranga bus station.
Ryan says there were crowds of about 60 people, and about a dozen buses.
"A lot of people were also on their phone to their bosses it sounded like, explaining they were going to very late to work - and lots of people just really frustrating and really fed up with the whole situation."
Metservice duty forecaster Georgina Griffiths said by 8am gusts would be about - or just under - the 80km/h mark.
"But it will be touch and go," she said.
"We will be monitoring it very carefully."
Griffiths said just before 7am, a cold front passed over the bridge - sending gusts that reached 98km/h.
At 7.30am, she said the city was seeing the worst of the situation - which might be some consolation for those Aucklanders sitting in traffic.
The MetService said the rest of the day would continue to bring gusts of up to 80km/h on the bridge and there would be strong northwesterly winds around Auckland.
Those wondering about tomorrow's commute will be happy to know that light winds are forecast in the city for the next three to four days.
Earlier, high-sided vehicles and motorcyclists were being strongly urged to avoid the bridge completely and instead use the Western Ring Route.
Traffic was building on State Highway 1 heading to the Auckland CBD.
Motorway cameras show bumper-to-bumper congestion on SH1 from Esmonde Road, Northcote Road and Tristram Ave.
It has been just over week since a strut on the bridge was damaged when a truck tipped over in a freak gust of up to 127km/h.
A temporary repair has been installed and work to put in a permanent fixture will not be complete for several weeks, NZTA said.
The annual event means closures for some lanes on the city's harbour bridge.