Indonesia's Sumatra island hit by 6.4 earthquake

A 6.4-magnitude earthquake struck off the coast of Indonesia's Sumatra island on Sunday but there were no reports of damage, the geophysics agency said.

"The epicentre is in the sea and there is no tsunami warning because at less than 7.0 magnitude it is still considered moderate," said Arif Nurahim, an official at Indonesia's Meteorology and Geophysics Agency.

The quake hit 640 kilometres southwest of Aceh province, which was shaken Wednesday by two massive earthquakes that triggered a tsunami alert.

At a magnitude of 8.6, the first of the two quakes was the strongest to hit since the 2004 Indian Ocean tsunami that killed 170,000 in Aceh but no major damage was reported.

Today's aftershock was not felt in Aceh, unlike the quakes last week which sent panicky residents pouring out of their homes.