People in Christchurch are being urged to keep warm. Three elderly people were taken to hospital with hypothermia on Monday night.
St John Ambulance says it responded to about 70 calls overnight and thousands were still without power on Tuesday afternoon.
Canterbury medical officer of health Ramon Pink says that makes heating challenging.
He says special efforts are being made to fix any gaping holes in houses and to get extra blankets to those who need them.
Residents are also advised to boil or treat water from taps or water tanks.