Mr. Key said in a television interview that crews would work through the night to find and rescue people who are trapped in the collapsed buildings. He said 350 military troops were already at work in the city and another 250 were on the way to relieve them.
The prime minister described seeing residents sitting by the side of the road with their heads in their hands and said the city of about 350,000 people is "in absolute agony." He said offers of help have been received from the United States and Australia.
Radio New Zealand reporter Laura Davis told VOA from Auckland that search-and-rescue teams were being flown in from around the country and that the government has accepted an offer of help from neighboring Australia.
She said 70 army medical staff have been deployed to help the city's overtaxed emergency crews and that up to 400 army troops had been sent to help seal off the most affected areas. The city's airport was shut down and many roads are impassible.
Davis also said schools had let out shortly before the quake and that many children were walking home when it struck. She said it was not clear what had happened to them.
The U.S. Geological Survey said the quake was centered five kilometers from Christchurch and at a depth of just four kilometers. Government seismologist Bill Fry told VOA that made it much more intense than the stronger quake that hit the city in September.
Fry explained that during the 10-second temblor, the ground was accelerating more rapidly "than the rate of an apple falling out of a tree."