Jakarta: A 5.7-magnitude earthquake on Monday struck off the coast of Indonesia's Sumatra island but there were no reports of damage, the geophysics agency said.

The undersea quake struck at 4:46 pm local time, with a depth of 10-kilometres, some 470 kilometres southwest of Simeulue island in Aceh province, the Meteorology and Geophysics Agency.

Aceh 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 1,70,000 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.