New Caledonia on Wednesday ordered the evacuation of coastal areas following a tsunami warning, after a powerful undersea earthquake of magnitude 7.6 struck off the east coast of the French territory.

The quake was just 10km deep and about 155km east-southeast of the Loyalty Islands, the Pacific Tsunami Warning Centre said.

Authorities in the South Pacific territory urged people to move to locations more than 300 metres distant from the shore, and if possible, to sites higher than 12 metres above sea level.

"We have set off the alarm on the exterior of New Caledonia but we don’t have any immediate assessment of potential damage," said a spokeswoman for the Directorate for Civil Protection and Risk Management.

"Tsunami waves reaching 1 to 3 metres above the tide level are possible along some coasts of New Caledonia and Vanuatu," the PTWC said, warning of possible waves of up to one metre for some parts of Fiji.

Eramet, the operator of the Doniambo nickel plant in New Caledonia's main harbour of Noumea, has triggered its tsunami alert process, a spokesman for the French mining and metals group said.

"The procedure is to ask people who work near the sea to move higher up," he said, adding that he had felt the quake, which he called strong, although it did not cause prolonged shaking.