A strong earthquake of 6.6 has rocked a north Indonesian island. No tsunami warning has been issued and there are no immediate reports of damages or casualties.

The U.S. Geological Survey says Saturday's quake struck 35 miles south-east of Palu city on Sulawesi Island at a depth of 12.6 miles. It hit at 17:41 local time.

Indonesia is prone to earthquakes because it is in the Pacific Ring of Fire, an arc of volcanos and fault lines encircling the Pacific Basin.