A 7.7 earthquake struck southeast of the loyalty Islands in the Pacific has prompted authorities in coastal areas of New Zealand and Australia to sound a tsunami alert urging public to avoid beaches and shore areas.

New Zealand authorities early on Thursday urged residents along its northern coast to avoid beaches and shore areas after a strong earthquake struck southeast of the loyalty Islands in the Pacific.

The New Zealand National Emergency Management Agency said people should get out of the water, off beaches and away from harbours, rivers and estuaries in areas from Ahipara to Bay of islands, Great Barrier Island and from Matata to Tolaga Bay.

"We expect New Zealand coastal areas to experience strong and unusual currents and unpredictable surges at the shore," the agency said in a statement.

Meanwhile, Australia's Bureau of Meteorology said there was a tsunami threat to offshore Australian islands and territories.

The European Mediterranean Seismological Centre (EMSC) said the 7.7 magnitude quake's epicentre was 417 km (258 miles) east of Tadine, New Caledonia, and was at a depth of 10 km (6.2miles)