John Mackie, the civil defence controller for Christchurch, said about 130 firefighters on the ground assisted by more than a dozen helicopters had stopped the blaze from encroaching further into the city.

He said the plan was to let it burn itself out, and that a forecast of rain over the weekend would help. He said the fire was spread over about 5,000 acres in Christchurch's Port Hills.

The cause of the fire remained unknown and was being investigated, he said.

A helicopter pilot who was a decorated soldier died in a crash while fighting the blaze earlier this week.

Corporal David Steven Askin had won one of the country's top awards for bravery for his actions in Afghanistan.

He was a member of the elite Special Air Service and his identity was kept secret when he won the Gallantry Star medal in 2014.

He was cited for efforts that included helping save guests during the 2011 siege of the luxury Inter-Continental Hotel in Kabul that left at least 20 people dead.

Christchurch City and adjacent Selwyn District declared a state of emergency on Wednesday. Selwyn Mayor Sam Broughton said changing winds had made the fire unpredictable.

He said the region had been unusually dry for three years and the grass in the hills had turned brown over the Southern Hemisphere summer.

Police ordered the evacuation of about 400 homes while many other people living nearby were choosing to leave. Mr Broughton said displaced residents were staying at evacuation centres or with relatives.

Phil Claude told Radio New Zealand he and his family ran down a grass track to escape the fire, which destroyed their home.

"I could see that the smoke and the flames were being blown right up toward our house," he said. "And I just yelled: 'Get out. Get out!'"

A new mountain bike park, the Christchurch Adventure Park, was threatened by the fire.

New Zealand's military was providing water tankers and engineering equipment as well as firefighters and other personnel.