A moderate 5.7 magnitude earthquake struck off the coast of Indonesia's Sumatra island on Saturday, U.S. geologists said, although there were no indications of a tsunami.

The quake struck at 9:59 pm local time and was relatively shallow, with a depth of 22 miles, the U.S. Geological Survey said.

The epicenter was 118 miles west of the port of Sibolga, in North Sumatra province.

An official at the National Quake Center, Muhamad Ramdan, said there were no immediate reports of casualties. "The quake epicenter was on the sea and there is no tsunami alert. People on Nias Island felt the tremor but there's no report of damage so far," he said.