SYDNEY, Australia - A 7.1 magnitude earthquake struck south of Vanuatu on Thursday, the United States Geological Survey said, triggering a tsunami warning.

The offshore quake hit at 1256 GMT at a depth of 48 kilometres (30 miles), about 123 kilometres south of the town of Isangel and 338 kilometres from the capital Port Vila, USGS said.

The Pacific Tsunami Warning Centre said "hazardous waves from this earthquake are possible within 300 kilometres of the epicenter along the coasts of Vanuatu and New Caledonia".

Vanuatu's Meteorology and Geohazards Department warned residents in the southernmost Tafea province to take "precautionary measures" such as moving from the coast to higher ground.

There were no immediate reports of damage.

USGS initially reported a magnitude of 7.3 and a depth of 35 kilometres, but soon revised its report.

Earthquakes are common in Vanuatu, a low-lying archipelago of 320,000 people that straddles the seismic Ring of Fire.

The Ring of Fire is an arc of intense tectonic activity that stretches through Southeast Asia and across the Pacific basin.

A magnitude 6.7 earthquake struck northern Vanuatu in November, with authorities warning that "small tsunami waves" had been picked up by ocean monitoring equipment.

Vanuatu is ranked as one of the countries most susceptible to natural disasters such as earthquakes, storm damage, flooding and tsunamis, according to the annual World Risk Report.