The quake struck just before dawn when few people were on the streets sending building facades crashing to the ground, crushing parked cars and showering the roads with shattered glass. Frightened residents fled from their homes to find streets covered in rubble and glass, but in the city of 340,000 only two people were seriously injured.
Many buildings were structurally damaged, and there were gas leaks, ruptured water and sewage mains, collapsed bridges and cuts to electricity supplies. A state of emergency was declared in the city with people being warned to stay away from damaged buildings for fear of further collapses as severe aftershocks continued to rock the city.
"I think we've been extremely lucky as a nation that there's been no fatalities... we're blessed actually," Civil Defence Minister John Carter said after being briefed on the impact of the quake. He described it as a "significant disaster" and although many Christchurch residents were in shock he appealed for people not to flood hospitals with minor injuries.
"The most important thing we can tell anybody at the moment is please don't panic," he said. Christchurch mayor Bob Parker said he was "horrified by the amount of damage" which daylight showed was considerably worse than first thought.
"We've decided to declare the state of emergency in the city. It just makes it a bit easier for us now to move people out of buildings if necessary, close streets down," Parker announced on national radio.
The quake, initially recorded at a magnitude of 7.4, struck at 04:35 am (1635 GMT yesterday) at a depth of five kilometres some 45 kilometres west of Christchurch, the US Geological Survey said.
"Oh my God. There is a row of shops completely demolished right in front of me," resident Colleen Simpson told the Stuff website, adding that many people had run out onto the streets in fear.