Jakarta - An undersea earthquake registering 6.5 on the Richter scale struck off Indonesia's central Sulawesi province on Monday, but there were no immediate reports of injury or damage, the Indonesian seismologist agency said.

The quake struck at 12:54 pm (0454 GMT) and its epicentre was about 196 kilometres south-west of Tolitoli, Indonesia's National Meteorology and Geophysics Agency said, adding that the quake occurred at about 33 kilometres below sea level.

Agency official Fauzi, who like many Indonesians uses only by one name, said there were no immediate report of injury or structural damage from the quake.

Indonesia, the world's largest archipelago nation, sits atop the Pacific Ocean's Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity. (dpa)