An earthquake measuring 7.9 has rocked the Pacific island of Tonga, although an initial tsunami warning has been cancelled after waves measuring less than one metre were recorded.

However the Pacific Tsunami Warning Center (PTWC) did confirm that a small tsunami "may have been destructive along coasts near the earthquake epicenter."

It also cautioned that "danger to boats and coastal structures can continue for several hours due to rapid currents."

It was not immediately clear what damage the earthquake may have caused, but reports say it was felt in several South Pacific islands.

The earthquake struck 155 km south of Tonga's Neiafu island and 2,145 km north east of Auckland, New Zealand at around 10:30 a.m. ET Wednesday, (4:26 a.m. local time on Thursday in Tonga) the U.S. Geological Survey website (USGS) said.

There are no reports of major damage to Nuku'alofa, the Tongon capital, according to The Associated Press. Power was restored about two hours after the quake.

Mary Fonua, a publisher in Nuku'alofa, told The Associated Press that it was the most powerful quake she had ever felt in Tonga.

"It was rocking and rolling, the floor was shaking, the whole family stood in the doorway and we heard crockery breaking in the kitchen and books fell from the shelves," she said.

"It's very dark and the power went off during the quake ... staff are reporting big flashes as the electricity grid went down during the shake and lines were broken."

Officials in New Zealand were placed on high alert after the quake, but Sgt. James Tasmania of Gisborne police told AP that "none of the (ocean) monitoring buoys have reported anything significant."

The Pacific Tsunami Warning Center (PTWC) initially warned that a tsunami wave could hit Suva, Fiji, as early as 5:13 a.m. local time, before affecting New Zealand's coastal cities in the following hours.

Tonga, a 170-island archipelago about halfway between Australia and Tahiti, has a population of about 108,000 and an economy dependent on pumpkin and vanilla exports, fishing, foreign aid and remittances from Tongans abroad.

Fiji, a South Pacific country made up of more than 300 islands, a third of which are inhabited, is regularly rattled by earthquakes, but few cause any damage or casualties.

A tsunami watch was issued for all other areas of the Pacific basin except for Alaska, British Columbia, Washington, Oregon and California.

In Dec. 2004, a magnitude 9.0 earthquake off Indonesia caused a tsunami across the Indian Ocean that killed more than 200,000 people in several countries.