About 70,000 people may have fled from Christchurch since last Tuesday's earthquake, says the city's mayor Bob Parker.
Mr Parker says he arrived at that number after contacting other centres in the South Island.
He says Timaru's mayor, for example, estimates 7000 people have gone there, while Queenstown estimates it has taken another 1000.
Up to 7000 Christchurch children have been registered at schools in places around the South Island, he says.
Mr Parker expects most residents will eventually return.
Meanwhile, Civil Defence officials believe as many as 21,000 residents could move to Auckland for a period of time after the earthquake.
Auckland's civil defence group manager Clive Manley says that figure is the top end of government estimates and includes people who might stay only briefly.
Mr Manley has told a routine civil defence committee meeting at Auckland Council that so far 2000 people have registered with help desks on arrival.
Some needed accommodation and more than 800 were given cash by Work and Income.