An earthquake with a revised magnitude of 6.6 struck 174 km (108 miles) north-northwest of the city of Ternate in Indonesia's Molucca islands on Sunday, followed by a series of aftershocks, but with no tsunami risk, the US Geological Survey said.

The quake hit at a depth of 60.5 km and was followed by aftershocks of a magnitude of 5.0 to 5.1.

Samud Sergi, an official from the search and rescue agency in Ternate, said the quakes had not been felt in the city.

A spokesperson for the emergency disaster agency in Tohomon for North Sulawesi said "they had felt nothing in the area and had heard of no damage or casualties".

An earlier report from the USGS gave the magnitude of the quake at 7.0 and the depth at 10 km.

The Pacific Tsunami Warning Center said in a statement that, based on available data, there was no current tsunami threat from the event.