An earthquake with a revised magnitude of 6.6 struck 173km northwest of the city of Ternate, North Maluku, in Indonesia's Moluccas islands, according to the US Geological Survey website.

The strong quake late early on Monday local time(late on Sunday GMT) hit at a depth of 60.5km and was followed by aftershocks of a magnitude of 5.0 to 5.1.

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

There were no immediate reports of damage or casualties and Indonesia's geophysics agency did not issue a tsunami alert.

"We felt the quake and some people got out of their house but there was no real panic. There is no damage in my area," a man from Ternate called Budi, who like many Indonesians goes by one name, told AFP news agency.

The city of Ternate has a population of around 200,000.

Bani Nasution, a man who was in the city of Manado when the quake struck, told AFP: "I ran out of my house and so did other people here, but we've all returned to our houses now."

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".

Indonesia is still reeling from a deadly tsunami at the end of December triggered by an erupting volcano in the middle of the Sunda Strait between Java and Sumatra islands that killed more than 400 people.

The vast Southeast Asian archipelago is one of the most disaster-hit nations on Earth due to its position straddling the so-called Pacific Ring of Fire, where tectonic plates collide.

The tsunami was Indonesia's third major natural disaster in six months, following a series of powerful earthquakes on the island of Lombok in July and August and a quake-tsunami in September that killed around 2,200 people in Palu on Sulawesi island, with thousands more missing and presumed dead.