NSW Police in Sydney's central business district. Photo / AAP
New Zealanders caught up in the area where a hostage drama is unfolding in central Sydney have spoken about their experiences.
Read more:
• Hostage drama: Siege at Sydney cafe
• Live updates
• Sydney siege photos
Up to 13 hostages are being held in an armed siege in a cafe in Sydney where an extremist flag is being held up in a window.
New Zealand-born Christy Johns said it was "terrifying" to experience.
The Channel 7 news producer was among those at the station who had to leave as the building was evacuated.
The network's newsroom is opposite the Lindt Cafe, and it is thought the gunman may have chosen the coffee shop for that reason.
"It's obvious that they wanted the media attention, because our Channel 7 offices in Martin Place just have one large glass window, and the Lindt Cafe is directly opposite it," she said.
"We could see straight over there, and see all the workers with their hands pressed up to the glass.
"We thought it was a hold-up at first, and then as soon as the flag went up our hearts just sank, and we realised that it could be really something else with the hostage situation."
Ms Johns, who was born in Christchurch and grew up in Brisbane, watched with colleagues as police descended on the building and began evacuating the surrounding offices.
"The police stormed the newsroom and we got evacuated upstairs to level 35," she said.
"Then we got evacuated, after about an hour, out of the building completely.
"She described going through "a little bit of stress, but the people inside [the cafe] they'll be going through a hell of a lot more".
"They would have been absolutely terrified, I'd say," Ms Johns said."They were just standing with their hands up on the glass, not moving. The guy inside got one of them to put up the flag."
It was unclear how many hostages there were, she said, but they could see four hostages standing against the three glass windows of the cafe.
"It's just insane," she said.
The Channel 7 employees had since been re-located to the station's headquarters at Jones Bay Wharf, in Pyrmont.
"Everyone's a bit shaken," she said.
"Hopefully it'll all end well, if it doesn't it'll hit hard I think, being there and seeing it all unfold from the start. But hopefully everything will be ok."
An armed policeman is seen outside a cafe in the central business district of Sydney. Photo / Getty Images
Aucklander Matthew Dale, 21, works in a restaurant on Bligh Street, near Martin Place, and was walking to start his shift when he came across the cordon.
He was standing in a crowd of about 200 people when he spoke to NZME. News Service.
"I can see a lot of armed police, dressed in black who look like the Armed Offenders Squad in New Zealand. There are detectives, too, in suits."
He said sirens were ringing out constantly as more police and officials arrived at the scene in Martin Place.
The atmosphere was tense and people were talking about the reports of an explosive device being inside the building, he said.
"I'm right outside the New South Wales Government Building, which is concerning. It is a little bit scary."
He said he hadn't be told to evacuate the area, but didn't expect many customers would be coming to the restaurant today.
Prime Minister John Key says he is unable to confirm whether anyone involved in the central Sydney siege is from New Zealand.
In a statement this evening he said agencies were at this stage unable to confirm the nationalities of those involved, including whether any New Zealanders were caught up in the siege.
Mr Key said authorities in New Zealand and Australia would continue to stay in close contact as events unfolded and facts became clearer.
The New Zealand Government was monitoring the situation in Sydney as events continued to unfold, he said.
Earlier today Mr Key said he contacted Australian Prime Minister Tony Abbott directly to offer a message of support.
"Our hearts go out to those involved and our thoughts are very much with them and their families," he said.
A spokeswoman for Mr Key earlier said New Zealand's national security system had been activated.
"Individual agencies will be assessing what they need to know and do," she said.
A Christchurch woman working two streets away from the cafe said her own building was in lock down and the area is "like a war zone".
A sniper sets up on Philip Street at Martin Place, Sydney. Photo / Getty Images
Armed policeman talk on Phillip St close to Martin Place, Sydney. Photo / Getty Images
Casey Harrison, who has lived in Sydney for the last four years and who works on George St, said a voice came over the loud speaker telling workers their whole building was in lock down and they were not allowed in or out.
"I'm two streets away [in a] 26-floor building. Looking down at the street is like a war zone, no one on the streets anymore, no cars, people are trying to get out as quick as possible."
All trains and buses had been halted and the opera house locked down too, as well as other buildings, she said.
"What we've also been told is they might shut down all phone networks to stop communication.
"At the moment [we've] been told to sit still and wait for the next instructions. I guess everyone's listening live on the comps [computers] - a lot got out early today - we can't go anywhere - on our floor there is least 1000. I honestly just want to go home. I am frightened, a lot of people are. There's a lot of mixed emotions, a lot of people think it might be a bit of an over-reaction."
Ms Harrison said public transport had been halted and she had no way of getting home.
Gary Graham, from Rotorua, works for an insurance company near Martin Place, which went into lockdown for several hours.
He told the Rotorua Daily Post about the tension people in the area felt.
"It's a strange feeling regarding what is happening. The police have closed down the street outside work."
His brother Sam Graham, who still lives in Rotorua, said he called his brother as soon as news about the seige broke.
"I was scared for his safety, that's why I called him as soon as I could. I'm just glad he's okay."
An armed policeman is seen on Philip St running from Martin Place in Sydney. Photo / Getty Images
Former Rotorua resident Kaylene Vokaty lived in Sydney for more than six years and used to work in Martin Place at a marketing company, but now lives in the Gold Coast.
Her best friend, cousins and former colleagues were in Martin Place at the time of the siege.
As soon as she heard the news, she called, messaged and emailed her loved ones to make sure they were safe.
Thankfully all of them were accounted for, she said.
"It's crazy, my colleagues and I used to always go to the Lindt Cafe. It was really popular and always so packed, people would queue for ages. It's just so hard to believe that this has happened. It's so frightening," she said.
"It's so close to home, it's really scary that this kind of stuff is going on here. It makes me want to get my family all together and hide in the safety of our home."
Two other New Zealanders in Sydney on business are just 20 metres away from the captive coffee shop.
Mum-of-two Kate Alexander and father-of-three Karna Luke are holed up in a building on Hunter St.
They had just walked from their central city hotel to a scheduled 11am meeting, walking past the Lindt coffee shop, when they commented how quiet it was for a Monday morning.
When they arrived at the building their meeting was, the doors were locked.
Security staff let them in and it was only then they were told of the armed siege underway just metres away.
Police secure the scene near Lindt Cafe, Martin Place, Sydney. Photo / Getty Images
"We're in lockdown. The police are evacuating building by building. When they get to us they will take us to a particular safe area," said Mrs Alexander, 44.
She can see a bomb squad, four fire enginges, about 15 firemen, and what she described as 'SWAT' teams.
"It's just gone extremely quiet," she said.
"The mood is very cautious, very quiet, people are very worried, I have to be honest.
"I'm ok... I'd obviously like it to be over, we're all a bit anxious. The way they have handled it does give us confidence though."
Arden Macdonald was staying in a hotel down the road from the scene of the siege and came across the cordon as it began.
The Virgin Australia cabin crew member is based in New Zealand but spent a couple of layover nights in Sydney.
Speaking from the cordon at the corner of Martin Place and Castlereagh St, he said the centre of Sydney's CBD was eerily quiet.
Police cars and evacuees are seen in Hyde Park due to a siege under way in Martin Place, Sydney. Photo / AAP
"Everyone's silent, if they're talking to each other they're whispering. You could hear a pin drop ... It's such a big chunk of the city [on lock-down]."
He said the crowd gathered at the cordon numbered about 200 people, and had the atmosphere of a vigil.
"There's police for Africa, but it's not like they've bombarded the place. There's no helicopters above the scene."
Kiwi Kate Hulbert, formerly of Napier, was sealed in her office building with her NobleOak Life Ltd colleagues after news of the siege broke.
"It's terrible, we are on lockdown and everyone is pretty scared, who knows what is going to happen."
She said they first heard a report of a hold-up at a store along Martin Place but didn't take too much notice of it.
"Then we heard siren after siren and the streets started to empty. It was scary, we knew then it was serious."
Her building was a couple of streets away from the Lindt store but armed police have confined her building's tenants to their offices after reports the gunmen had explosive devices, she said.
"The scary part is they are saying there are bombs planted around the city so they could be anywhere -- there is no one on the streets, it's just a complete ghost town. Everyone is just too scared to go outside."
She said police have placed warning signs on all the buildings within the siege zone, while office workers have also been told to stay away from windows and doors.
"We are just sitting around a TV watching the news -- watching Tony Abbott, waiting."
Australian Bunnings footage shows attacks on staff members in store.