EVACUATIONS were underway in coastal areas of New Zealand after a tsunami warning was issued following a powerful 7.1 magnitude earthquake.

An initial "potential" warning was upgraded to a tsunami after a wave measuring 30 centimetres was generated near East Cape about 90 minutes after the earthquake struck off the east coast of the North Island.

It is said the jolt which lasted for almost a minute was felt by thousands across much of the North Island.

"The first tsunami activity has arrived. Tsunami activity will continue for several hours," the Civil Defence organisation, responsible for national emergency management, said in a statement.

The warning covered the East Coast of the North Island and the upper South Island.

Radio New Zealand reported that Civil Defence officials had warned anyone living near the east coast to leave their home, take the radio and go to higher ground. Later they said some residents could return home.

In a statement Civil Defence confirmed that following instructions from local civil defence authorities, some ome communities north of Gisborne self-evacuated following the earthquake "which was the right thing to do".

Officials said: "If you feel further shaking which is too strong to stand up, or over one minute in duration, move to higher ground immediately."

There was also a warning for people to stay away from beaches and remain out of the water, including sea, rivers and estuaries.

Just a month ago, New Zealand was involved in a civil defence exercise called Exercise Tangaroa, to test the country's ability to respond to and recover from a major tsunami.

Over a hundred organisations around the country took part, including emergency services, local and central government, utility providers and the private sector.