A large office block in Wellington is at significant risk of collapse with a major supporting beam "like a broken bone".
A section of Molesworth St that includes Wellington Cathedral of St Paul, the National Library and NZ Rugby headquarters and the Thai embassy has been cordoned off, with people cleared from the area.
The office block at 61 Molesworth St has been vacant because of renovation work. An engineer involved approached the fire service today, concerned about a structural beam.
Fire Region Manager Brendan Nally said it was unlikely office workers and residents in buildings within the cordoned-off areas would be let in tomorrow.
"We have a clear structural failure. What's caused that will be determined later.
"The clear structural failure is a major beam - a vertical beam in the building - has been shorn.
"It looks somewhat like a broken bone in the leg. It is fractured through. It is a major supporting beam. It is up above the fifth floor, so it is the top four floors."
That assessment was being done using cellphone photos, the fire service said. The cordon was big enough so that if the building did collapse it would be contained within it.
The building looks to be about 10 stories tall.
Members of the Diplomatic Protection Squad (DPS) - normally accompanying the Prime Minister at neighbouring Parliament - were on the scene helping direct traffic at the Hill St intersection.
Corinne Ambler works in the New Zealand Red Cross situated next-door to the Molesworth Tower and said staff were told to evacuate immediately.
"It's a bit more drama just to add to the earthquake, the flooding and the wind," she said.
"The receptionist came running through every floor of the building saying 'I've just been told that we have to evacuate, there's a very tall build next door to ue... and that it could be in danger of collapsing on top of the NZ Red Cross building'.
"So we all as as fast as we could grabbed our stuff and we were out of the building in a couple of minutes, and we're all standing out on the street here."
Ambler said the building had "definitely slumped".
"It's a big building with two parts to it, there's a concrete column... in between the concrete column and the rest of the building is like a glass conservatory and that you can definitely see has sunk, there are bits of glass and panes of glass missing.
"It's lumped in the middle, if that concerete slab breaks away... then that could fall on top of our building."
She said the building looked as though it was unoccupied, but food outlets and cafes at the bottom floor were rapidly moving their stock.
"There are a whole lot of small businesses, and cafes underneath it and just after we evacuated all the small business owners were parking their cars up out front and running their supplies into the boots of their cars, sacks of rice, food everything."
The building is listed as an eight-story office tower with five small retail units and a reception at ground level, with space for parking on a first-floor podium.
According to the website of Archaus Architects, who were engaged to redevelop the commercial property, the renovation work would increase the rentable office area to about 1340m2 per typical office level, and increase the building height to 43.8m, providing an additional 2 levels.