It is estimated that about 70,000 people, or a fifth of Christchurch's population, have fled the city since the earthquake on 22 February.
Christchurch Mayor Bob Parker is one who thinks as many as 70,000 have left.
Airlines and ferry companies say there has been a significant uptake of their services by Christchurch residents leaving the city.
Air New Zealand says it has flown about 60,000 people out of Christchurch since Wednesday 23 February.
Cook Strait ferry operators Interislander and Bluebridge say they have had an influx of additional passengers and vehicles.
Deputy Mayor Ngaire Button says people are sure to come back, because for many who have fled, Christchurch will still resonate as the place where they belong.
Auckland expects 21,000
Civil Defence in Auckland says the city's health sector predicts a short-term population increase of 21,000 as a result of the displacement.
Auckland's Civil Defence controller, Clive Manley, says the Auckland Council is working closely with the sector to ensure it is ready to help those coming from Christchurch.
Mr Manley says the city's welfare services are also open to those who are supporting the displaced people.
Housing New Zealand says it is still tallying up how many Christchurch tenants it has helped to rehouse around the country.
Timaru's population swells
Just as Christchurch's population has diminished by a fifth, Timaru's has gone up by a fifth as a result of the diaspora from the north.
Timaru Mayor Janie Annear says her city is having to find ways of coping with the sudden influx.