Damage to a central Wellington building is getting worse and a significant aftershock would dramatically increase its risk of collapsing, officials say.

Cordons remain in place around the building at 61 Molesworth St, near Parliament, with the street and neighbouring businesses remaining shut on Wednesday until another inspection of the building takes place. One of the building's main support beams snapped in half after Monday's magnitude 7.5 quake near Kaikoura rocked the capital.

Wellington City Council general manager of building control, Mike Scott, said on Wednesday photographs from before and after an aftershock showed the building had moved and that was a concern. "It has got incrementally worse."

Several different engineering firms were assessing the safety of the former Deloitte building and the cordon would stay in place till further notice, but he was confident there would be no casualties if the tower did tumble, he said. 

"Life safety is our absolute paramount concern," Scott said.

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MONIQUE FORD/FAIRFAX NZ

The damage to the building on Molesworth street is getting "incrementally worse" officials say.

Owners of the office block were working with the council to go through safety concerns, Scott said.  "This isn't going to be a quick fix."

A superficial inspection had shown one column in the building had broken in two, and that was the main cause of concern. 

"We're worried about ongoing earthquakes and it's actually about the structure of the building, not the ground it's sitting on," Scott said.

Urban Search and Rescue were hoping to send a senior structural engineer in and it was hoped the building could be inspected on early Wednesday afternoon and monitoring equipment put inside.

Elsewhere in the city, Scott said no obvious trend could immediately be discerned what building types or ages had been worst affected.

"It's been all over the shop...different building types across the whole spectrum have been affected differently."

He said residential tenants with concerns about building safety needed to get in touch with insurers or engineers as soon as possible.

The building on Molesworth street before the earthquake (L) and on Tuesday.

"If you've got any concerns about the safety of your building you need to engage somebody yourself."

"If you're concerned as a tenant, I suggest you actually get some legal advice.

"We've had the odd comment that commercial building owners have just done the broad sweep and said 'no, it's fine, you can go back in.'"

But he said commercial property owners had generally been conscientious.

MONIQUE FORD/FAIRFAX NZ

The building on Molesworth Street was at risk of collapse.

Meanwhile, safety concerns remained in Featherston St, but Scott said authorities had significantly reduced the cordon there.

EMERGENCY EVACUATION

On Tuesday, engineers declared the 8-storey Molesworth St building to be "at significant risk of collapse", and it and adjacent buildings were hurriedly evacuated about 5pm. There was no movement from the building overnight.

Only a handful of volunteers remained at the scene early on Wednesday morning.

Molesworth St, between Hill St and Hawkestone St, would remain cordoned off until further notice.

The street was a major thoroughfare for cars and buses, and its closure would disrupt traffic from Thorndon and surrounding suburbs, as well as from the Hutt Valley and other areas north of Wellington.

Workers in the immediate area should check with their employers about whether their office would be open on Wednesday.

BRAD FLAHIVE/FAIRFAX NZ

Cordons were in place and nearby buildings were evacuated.

​Affected buildings included the Thai embassy, the New Zealand Rugby headquarters, two shops - The Mews and a sushi store, the National Library, Red Cross offices, and the Wellington Cathedral of St Paul.

A number of private houses accessed off Collina Terrace were also evacuated due to the risk of collapse.

The notice being handed out to residents on Molesworth St.

'LIKE A BROKEN BONE'

On Tuesday evening, regional Fire Service chief Brendan Nally said the vertical beam looked "somewhat like a broken bone in the leg."

"It's fractured through - it's a major supporting beam. It's up above the fifth floor, so it's the top four floors of the building."

Leasing agents advertised the Molesworth St building as "to be extensively refurbished and strengthened to 100% NBS (New Building Standard)", although no timeframe was given for that work.

Its current NBS rating was not known; however, it was not on the Wellington City Council's list of quake-prone buildings.

 - Stuff