A 5.9-magnitude earthquake hit the north of Indonesia's Sumatra island on Saturday, the US Geological Survey said, but there were no reports of damage or casualties.

The quake struck at 11:34 am (0434 GMT), 66 kilometres (41 miles) west-southwest of Kabanjahe at a depth of 97 kilometres, the USGS said.

Indonesia's Meteorological and Geophysics Agency put the magnitude at 6.6.

"The quake's epicentre was on land. There are no reports of damage so far," Indonesian agency official Dedi Sugianto told AFP, adding the quake was felt moderately in a number of areas.

Indonesia sits on the Pacific "Ring of Fire" where continental plates collide, causing frequent seismic and volcanic activity.