Maruschke Barnard had time only to grab a dressing gown and her 5-month-old baby when residents of Clifton Hill, Sumner, were suddenly evacuated from 7am yesterday.

Mrs Barnard, 21, had no time even to find her shoes and purse.

Her parents, Joseph and Hannalie Viljoen - who Mrs Barnard, her husband Evert and baby Dianthe-Rose live with on the hill - learned of the evacuation as they left for their jobs on the unaffected side of the city.

Police at the bottom of the hill told them: "'Mate, get off this hill, it's going to come down'," said Mrs Viljoen.

Authorities were already at their home by the time they rushed back. Important papers, such as passports for the immigrant South African family, were left behind.

Mrs Barnard said: "It was that quick - please get out now!"

The decision was made after geologists decided the hill was unstable. All residents from Clifton Terrace down had to leave while those in streets higher on the hill have been told to stand by for possible evacuation.

In Sumner, Senior Sergeant Scott Banfield said Christchurch City Council's "geo experts" had decided Clifton Hill was dangerous. "Overnight, the danger to people on Clifton Hill became quite obvious."

A temporary base was being set up quickly at the old school hall on flat land behind Sumner village for evacuees.

Radio New Zealand said 60 people had been moved off the hill by noon yesterday but many had already left for safer places. One street was evacuated last Thursday.

Today police said most of the Clifton Hill residents who were evacuated yesterday were allowed home last night about 6pm.

Senior Sergeant Murray Hurst said engineers had given the hillside the all clear.

About 10 residents whose homes had been declared uninhabitable were not able to return, he said.

The Viljoens said the earthquake hadn't made them reconsider moving to New Zealand from South Africa. Their granddaughter was born one minute after the September earthquake and has known nothing other than tremors as thousands of aftershocks have since rattled the city.

"I'd rather go through all the shaking than have those other problems back in South Africa," Mrs Viljoen said.