SUVA, Jan. 24 (Xinhua) -- An earthquake with a magnitude of 6.3 jolted 43 km SW of Port-Vila, Vanuatu, at 1:33 local time on Wednesday, the U.S. Geological Survey (USGS) said.

       There were no immediate reports of casualty or damage.

       The epicenter, with a depth of 37.2 km, was determined to be at 18.009 degrees south latitude and 168.016 degrees east longitude, according to the USGS.

       The Pacific Tsunami Warning Center did not immediately issue a tsunami warning based on the quake.

       Pacific island countries such as Fiji, Tonga and Vanuatu lie on the so-called Pacific "Ring of Fire," an arc of earthquake and volcanic zones where continental plates collide, producing frequent seismic activities.