SYDNEY -- A 5.9-magnitude earthquake struck off the south Pacific island of Vanuatu early Friday, the US Geological Survey said, but there were no early reports of damage or casualties.

The quake hit at 4:31 am (1731 GMT Thursday), 80 kilometers (50 miles) west of Port Vila, the capital city of Vanuatu, at a depth of 50 km, the USGS said.

No tsunami warning was immediately issued.