New Zealand Prime Minister John Key says 65 people died in the earthquake that devastated Christchurch today.

''The death toll I have at the moment is 65 and that may rise. So it's an absolute tragedy for this city, for New Zealand, for the people that we care so much about,'' Mr Key told TVNZ. ''It's a terrifying time for the people of Canterbury.'

He said: "We may be witnessing New Zealand's darkest day."

Emergency workers including those from Auckland are still searching for survivors.

The 6.3 magnitude quake - classed by experts as an aftershock to last September's 7.1 quake - struck at 12.51pm (10.51am AEDT).