General view as smoke and fire light up around Worsleys Road on February 15, 2017 in Christchurch, New Zealand. A wind change has caused homes near the Port Hills fires to be evacuated, with firefighters saying the situation is highly volatile. One person has died, and buildings, vehicles and forestry have been destroyed from the Port Hills fires, which have been raging since Monday afternoon. [Photo/VCG]

WELLINGTON - More than 1,000 people were evacuated from their homes and a state of emergency was declared in New Zealand's third largest city of Christchurch on Thursday because a wildfire threatens homes.

The fire in the Port Hills district of the city began earlier this week but spread rapidly overnight to cover more than 1,800 hectares (4,447.9 acres), emergency workers said.

Prime Minister Bill English canceled all his engagements to set off for Christchurch to monitor developments.

"The situation remains very serious," said David Adamson, Christchurch Civil Defence Controller. "Police and the Defence Force have had a huge job overnight with evacuations, the setting-up of cordons around key areas and security patrols of areas that have been evacuated."

Fifteen helicopters and fixed wing aircraft, the maximum number that can safely be in the air at any one time, have been despatched amid forecasts for winds that could fan the flames.

A change in the wind direction is predicted for later in the week that will lower temperatures and humidity and could slow the fire's progress, emergency workers said.

A helicopter pilot died on Tuesday after crashing while tackling the blaze.