A strong undersea earthquake has struck off eastern Indonesia, but there were no immediate reports of casualties or damage and no tsunami warning was issued.

The U.S. Geological Survey says the magnitude-6.3 quake that struck Wednesday afternoon was centered 140 kilometers (87 miles) northeast of Bitung, a coastal town on Sulawesi island, and had a depth of 53 kilometers (33 miles).

Indonesia's Meteorology and Geophysics Agency says the quake did not have the potential to cause a tsunami.

Indonesia, the world's largest archipelagic nation, is prone to seismic upheaval due to its location on the Pacific "Ring of Fire," an arc of volcanoes and fault lines in the Pacific Basin. In 2004, a massive earthquake off Sumatra island triggered a tsunami that killed 230,000 people in a dozen countries.