MANILA, PHILIPPINES - A powerful earthquake struck at sea off the central Philippines on Friday, but there were no immediate reports of casualties or damage, seismologists said.

The US Geological Survey said the quake had a magnitude of 6.0 and struck in the South China Sea off the west coast of Mindoro island at 2:23 pm (0623 GMT).

Local seismologist Ismael Narag said the quake generated enough power to unleash big waves, but added that no warning was issued because authorities did not think it was capable of triggering a tsunami.

'It would have to be at least 6.5 magnitude to generate a tsunami,' said Narag, from the Philippine Institute of Volcanology and Seismology.

The quake occurred about 50 kilometres (31 miles) beneath the sea surface, according to a US Geological Survey advisory.

It said the epicentre was about 30 kilometres off Calintaan, a western Mindoro town of 24,000 people.

Police in the province of Occidental Mindoro, where Calintaan is situated, said that, although the quake was quite strong, they had no reports of any damage to the region's isolated and sparsely populated west coast.

'It was a strong earthquake and it lasted for quite a while,' officer Rose Macabenta told AFP by telephone from provincial police headquarters.

'It rattled the tabletops, but the wall frames stayed in place,' she said.

Calintaan police could not be immediately reached for comment.