Sydney: A strong 6.4-magnitude earthquake on Saturday struck off the Pacific nation of Tonga, US seismologists said, but there were no immediate reports of damage and no tsunami warning was issued.

The quake happened at 11:08 PM (1008 GMT) 78 kilometres from the town of Neiafu, on the south coast of the island Vava'u, at a depth of about 130 kilometres, the US Geological Survey (USGS) said.

The USGS had initially said the quake had a magnitude of 6.7.