New Zealand Prime Minister John Key has left Whenuapai Air Force base on a flight bound for Christchurch to view the damage caused by Saturday's 7.1-magnitude earthquake.

The small King Air plane he is on will stop in Wellington to pick up other government ministers, including Civil Defence Minister John Carter and local MP Gerry Brownlee, Radio New Zealand reported on Saturday.

Shortly before midday, an Air Force Hercules left the Whenuapai base with 20 search and rescue crew on board.

Both planes have military waivers to land at Christchurch Airport even if it is still closed.

Meanwhile, Carter has advised people to keep calm, not to panic, and to be sensible.

People should check on their friends and neighbors to make sure they are safe, but he requested that people not over-use the cellphone and communications systems, as they could collapse.

It is a blessing no one died in the massive earthquake, Carter said after crisis meetings in the government building.

"I think we've been extremely lucky as a nation," Carter told media after top public servants, ministers and specialists met in the wake of the major quake, which hit across Canterbury about 4: 35 a.m. local time, with several severe aftershocks.

Buildings crumbled throughout Christchurch, and in rural Canterbury, crushing cars and closing roads, yet only one serious injury was reported, a man in his 50s who is in intensive care in Christchurch Hospital.

A state of emergency has been declared in Christchurch and the Selwyn districts, with 90 percent of power expected to be restored by Saturday evening, but water and sewage would take longer to get back in order.

Civil Defence headquarters has activated the national crisis center. No tsunami alert has been issued.