The earthquake's epicentre was 26 kilometres (16 miles) deep, the USGS said. It was 135 kilometres (84 miles) from Isangel in Vanuatu and 147 kilometres (91 miles) from the Loyalty islands, part of the French territory of New Caledonia.
The Pacific Tsunami Warning Center said in an evaluation that "no destructive widespread tsunami threat exists based on historical earthquake and tsunami data".
John Servo, an official at the Vanuatu Meteorological Service, said there was unlikely to be any damage.
"We felt it on Vanuatu, of course, but it was not strong," he told AFP.
"There has been no tsunami warning and we don't expect any damage. It was too far away."
Vanuatu, which lies between Fiji and Australia, is in the "Pacific Ring of Fire", known for its high seismic and volcanic activity caused by friction between moving plates in the Earth's crust.
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