A tsunami warning has been issued for the Solomon Islands, Vanuatu and Papua New Guinea, the Pacific Tsunami Warning Center said.
The Center said the warning was issued based on the magnitude of the quake, and is was not known whether a tsunami had in fact been generated.
The USGS said the quake — which it had initially assessed at 7.7 — occurred at 11.36pm local time (12.36 GMT) at a depth of 35km, 111km south of Kirakira in the Solomon Islands.
It said the likelihood of casualties or damage was low. A 7.6 magnitude quake had woken the residents of the Solomons capital Honiara early today.
It struck at 7:14 am, about 300 kilometres from the capital, and was followed 10 minutes later by a 5.9-magnitude aftershock.
The US Geological Survey measured the undersea quake at around 29 kilometres deep.
Honiara resident Dorothy Wickham said the national disaster council was warning people to stay away from low-lying areas as the islands experienced high waves.
"People are moving away from the coasts and are going up into the hills, but I have not heard of any damage," she said.
The Intergovernmental Oceanographic Commission put out a tsunami warning for the Solomon Islands, Vanuatu and Papua New Guinea following the Sunday morning quake, but later cancelled the alert.
The Solomons were hit by flash floods 10 days ago which left more than 20 dead. Several more are still missing in Honiara after the city's main river burst its banks following days of heavy rain.
The Solomons are part of the "Ring of Fire", a zone of tectonic activity around the Pacific that is subject to frequent earthquakes and volcanic eruptions.
A 6.1-magnitude tremor hit the Solomons yesterday and a powerful 7.1-magnitude earthquake and 6.7 aftershock struck off Papua New Guinea's Bougainville island on Friday, to the west of the Solomons.