More than 1,000 people have been evacuated from their homes and a state of emergency declared in the New Zealand city of Christchurch as a raging bushfire headed into its fourth day.

Key points: At least 11 houses have been destroyed by the fire which has spread to cover more than 1,800 hectares

At least 11 houses have been destroyed by the fire which has spread to cover more than 1,800 hectares NZ PM has cancelled engagements to monitor developments

NZ PM has cancelled engagements to monitor developments Change in wind direction later in the week could slow fire's progress

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, emergency workers said.

At least 11 houses have been destroyed.

"Yesterday we were chasing a monster — we were trying to catch it, and you add in wind and it becomes totally uncontrollable," emergency management spokesman Richard McNamara told Radio New Zealand.

"Yesterday afternoon some of the fire behaviour was some of the worst I've [ever] seen, and I've seen fire behaviour in the western US and Australia."

Sorry, this video has expired New Zealand bushfires: 'We thought it was under control'

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

"The situation remains very serious," Christchurch Civil Defence Controller David Adamson said.

"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."

Sorry, this video has expired At least five houses have been destroyed by the fires (Photo: Twitter/howesaman)

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.

More than 200 firefighters are battling the blaze.

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.

Sorry, this video has expired Man forced to flee Christchurch bushfire

Reuters/ABC