New Zealand Civil Defence has warned people in coastal areas to stay off beaches due to the risk of a tsunami caused by a 7.7 magnitude earthquake in the Kermadec Islands region.

The 7.7 magnitude quake struck at a depth of 48km in the Kermadec Islands region, which is 800-1000km north of New Zealand, at 7.03am NZT (5.30 AEST).

The tsunami warning applies to New Zealand, the Kermadec Islands and Tonga and the tsunami caused by the quake is scheduled to reach the East Cape of the North Island and North Cape just before 9am NZT and Auckland at 10am.

A spokesman from the Pacific Tsunami Warning Centre said the wave generated by the quake was 60cm high.

A statement from Civil Defence said it had confirmed a tsunami had been generated by the quake and there was a marine threat to Northland, Bay of Plenty, East Coast and Hawkes Bay.

It said the "first wave to arrive to New Zealand will be in the areas around at approximately 8.52am (6.30 AEST)," but possibly later .

It said the first wave "may not be the largest" and the waves would continue for several hours.

It warned people to stay off beaches and stay out of the water - including the sea, rivers and estuaries and boating activities - as long as the alert remained in force.

People have also been advised to follow the instructions of local Civil Defence authorities, listen to the radio and TV for updates and share information about the alert with family, neighbours and friends.

The advisory would remain in effect until it is upgraded to a national warning or a cancellation message is issued by Civil Defence.

Scientific advisers were closely monitoring the situation to determine the severity of the threat to New Zealand and more information would be released within the next hour.

Until a cancellation is issued, updates would continue at least hourly, the Civil Defence statement said.

The National Crisis Management Centre has been activated and local Civil Defence authorities were acting in coordination with the national centre.