A magnitude 7.8 earthquake struck off the Solomon Islands early on Friday, triggering a tsunami warning across a wide area of the South Pacific.

The quake struck at 4:38 a.m. (17:38 GMT Thursday) at a depth of 40 km (25 miles), the US Geological Survey said. It was initially reported to be of magnitude 8.0.

There were no immediate reports of damage or casualties.

"Hazardous tsunami waves from this earthquake are possible within the next three hours along some coasts of Solomon Islands, Vanuatu, Papua New Guinea, Nauru, New Caledonia, Tuvalu and Kosrae," the U.S.-based Pacific Tsunami Warning Center (PTWC) said.