JAKARTA, INDONESIA - A strong 6.2-magnitude quake struck off Indonesia's Sulawesi island Tuesday but there were no immediate reports of damage and no tsunami warning was issued, the country's geophysics agency said.

The quake struck at 8:38 pm at sea 195 kilometres southeast of Melonguane in North Sulawesi province at a depth of 18 kilometres, the agency said in an SMS alert.

"The quake has no tsunami potential. We are still trying to determine... if there are any casualties," agency technical chief Suharjono said.

Indonesia sits on the Pacific "Ring of Fire," where the meeting of continental plates causes high volcanic and seismic activity.

A quake in West Sumatra province late last month killed 809 people, according to official figures. But the United Nations has said the toll is likely to be over 1,100.