Jakarta - A powerful undersea earthquake measuring 6.6 on the Richter scale shook parts of eastern Indonesia Thursday morning, but there were no immediate reports of damage or casualties.

The quake struck at about 5.41 am local time with its epicentre about 51 km northeast of Sumbawa Island, according to an official report from the Jakarta meteorology and geophysics agency.

The quake was 10 km beneath the seabed, but there were no immediate reports of tsunami or structural damage from the latest in a series of earthquakes to strike Indonesia in recent days, the report said.

Indonesia, the world's largest archipelago nation, sits atop the Pacific Ocean's Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity.

In December 2004, a 9.1-magnitude quake triggered a tsunami that struck nine countries. The waves killed some 177,000 people in Indonesia's Aceh province alone.