WELLINGTON (AFP, REUTERS) - A wildfire destroyed at least 11 homes and forced hundreds of terrified residents to evacuate in the New Zealand city of Christchurch, authorities said Thursday (Feb 16).

Civil defence officials declared a state of emergency in the South Island city late Wednesday as two blazes that had been smouldering for days merged into a single giant fire-front.

Christchurch City Council said more than 1,800 hectares of land had been torched in the Port Hills, an area of rugged and difficult to access terrain to the east of the city centre.

About 1,000 people had been evacuated. "There's a whole lot of people here who have been traumatised by the events, some who have lost their homes, many have been evacuated," Prime Minister Bill English told reporters in Christchurch after cancelling all his engagements to fly to the city.

He said it could take up to a week before the fire was fully under control, but that the blaze had been contained on Thursday and was not spreading further.

But, with winds forecast to pick up and fan the flames, authorities warned residents to flee at the first sign of danger.

"We understand it's hard for people to leave their homes but the fire can change direction and move incredibly quickly," senior sergeant Ash Tabb said.

"If you're worried, don't leave it too late - it's better to be safe than sorry."

With a thick pall of smoke hanging over Christchurch, residents with respiratory ailments were advised to stay indoors.

Wildfires of such ferocity are rare in New Zealand, where regular rainfall usually prevents them reaching the intensity seen in places like Australia and the US west coast.

The emergency has so far claimed one life, when a helicopter that was dumping water on the flames crashed Tuesday and killed pilot Steve Askin, a decorated special forces veteran.

Civil Defence said it had confirmed 11 homes had been razed but added the situation was constantly changing.

It said 14 helicopters and three planes were helping battle the blaze, the maximum number of aircraft that could safely operate around the fire-front at one time.

Some 200 firefighters were operating about 45 pumps and tankers on the ground, with police and the military also providing additional personnel to the emergency response.

Civil defence said weather conditions were forecast to ease on Friday, slowing the fire's progress.