A resident heard a "big crack" before a landslide tumbled onto The Terrace in central Wellington, threatening two homes.

Three fire crews are at the scene and police are assisting with traffic management.

One resident, who wished to remain anonymous, said they heard a big crack and thought a branch from a nearby pine tree had fallen.

"I went outside to take a look and the whole bottom of our stairs had been ripped away and there was just a big hole."

When they went down to investigate there was a "hissing sound but no water".

When emergency services arrived they told everyone to get out and that there was a gas leak, they said.

The resident said they had left everything inside the house, including a work laptop and wallet.

Fire crews at the scene. Photo / Nick James

Reflecting on the afternoon, the resident said- "that's Wellington I guess."

Wellington City Council spokesman Richard MacLean said the slip was "a biggie".

It was on the section of The Terrace between Ghuznee St and Buller St, he said.

"It's blocking the whole road and it looks like it has brought down a big concrete retaining wall," MacLean said.

MacLean advised motorists and pedestrians to stay away from the area.

Fenz district manager Nick Pyatt said two properties have been evacuated, but was unsure at this stage how many people were affected.

"We're awaiting the arrival of a geotech and structural engineering team who will monitor and assess the ability of the land to hold that building up there."

Emergency services near the scene. Photo / Nick James

They were working with the city council to find accommodation for people, Pyatt said.

Pyatt estimated the slip was about 4m deep and fire crews were keeping a close eye on a large tree that had possibly been undercut.

A couple of gas pipes were severed when the landslide came down, but they have since been isolated, Pyatt said.

- Georgina Campbell and Nick James, NZ Herald