A shallow, 6.6-magnitude earthquake has hit inland on the central Indonesian island of Sulawesi, US seismologists said, causing people to panic and run out of their homes.

There were no immediate reports from officials of casualties or damage after the quake, which USGS said hit at a depth of 9km at 10.35 pm, 80km from the city of Palu.

But Muhammad Guntur, who lives on the outskirts of Poso, east of the epicentre, said it was felt strongly.

"People are panicking here. We are now all gathered outside of our houses," he told AFP. "The electricity is off here."

A hotel worker in Poso also said that people panicked when the quake struck but that things had returned to normal there.

"The electricity was off for a while," said the worker Buhory, who like many Indonesians goes by one name. "People were panicking but now it is on again and everything is okay."

Indonesia's Meteorology, Geophysics and Climate agency -- which monitors quakes -- said it was still assessing the impact.

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

An earthquake struck Indonesia's western Aceh province in December, killing more than 100 people, injuring many more and leaving tens of thousands homeless.

The quake hit in one of the areas worst affected by the devastating Indian Ocean tsunami in 2004.