Port Vila: A strong 6.4-magnitude earthquake struck the Pacific nation of Vanuatu Friday, the US Geological Survey said, but there was no risk of a widespread tsunami.

The quake hit at a depth of about 35 kilometres (22 miles) with an epicentre 222 kilometres northwest of the port city Luganville, known locally as Santo just after 5pm local time (0600 GMT), the USGS said.

The Pacific Tsunami Warning Centre said there was no threat of a destructive widespread tsunami, based on historical earthquake and tsunami data.

"However, earthquakes of this size sometimes generate local tsunamis that can be destructive along coasts located within 100 kilometres of the earthquake epicentre," it said in a bulletin.

Clive Collins, a seismologist at Geoscience Australia, said the quake was unlikely to cause damage or injuries.

"It's well away from land as far as we can see," Collins told AFP, adding that it looked to be "right in the middle of the sea".

"It's probably too far away and it's reasonably deep too so we don't expect any strength from that," he said, adding that Geoscience Australia had assessed the quake to be a magnitude 6.8 and at a depth of 66 kilometres.

Vanuatu lies on the "Pacific Ring of Fire", known for its seismic and volcanic volatility owing to friction between giant, moving plates in the earth's crust.

A 7.2 earthquake hit the archipelago, which lies between Fiji and Australia and north of New Zealand, in May, prompting a brief tsunami alert.

The country was hit by three major quakes last October, while a giant plume of volcanic ash has disrupted domestic flights in neighbouring New Caledonia in recent months.