Major quake rocks New Zealand, tsunami alert issued

But a statement stressed it was not an emergency warning yet, and advised the public to monitor radio stations for more information.

Although there were reports of cracked walls and items toppled from shelves in the Southland province, there were no immediate reports of serious damage or human casualties.

New Zealand seismologists said the quake measured 6.6 but reports from the US Geological Survey registered it at 7.8, and another measurement put it at 8.2, according to a local civil defence official.

The quake at 9.22 pm was followed soon after by another which New Zealand's GNS Science said measured 6.1 on the Richter scale.

It was centered off the coast 90 km southwest of the lakeside resort town Te Anau in Fiordland, but was felt 300 km away in Dunedin, Radio New Zealand reported.

There were no immediate reports of serious damage.

"Everything was moving, it went on for a long time," Simon Wilson, a resident of the southernmost city of Invercargill, 150 km from the focal centre, told Radio New Zealand.

"The whole house was moving, the door and the door frame was moving, the fence posts were moving - it was a big one."

But he said his house was not damaged.