A strong earthquake rattled Indonesia's Sumatra island (search) Monday, where thousands fled to high ground a day earlier after another powerful temblor triggered unfounded fears of a tsunami (search).

Seismologists in Hong Kong (search) said the 6.1-magnitude quake's epicenter was about 167 miles south-southwest of Medan in western Sumatra. The tremor hit at 0617 GMT, the report said.

On Sunday, thousands of people who left their homes in the west Sumatran city of Padang after a 6.8-magnitude temblor and a series of smaller aftershocks.

Seismologists predicted they would continue for several days.

Hong Kong seismologists registered a 6.0-magnitude quake at 1730 GMT Sunday.

Sunday's undersea 6.8-magnitude temblor smashed scores of windows in Padang, and was felt across a large swathe of Sumatra, which was devastated by the Dec. 26 earthquake and tsunami that at least 174,000 people in 11 countries and left another 50,000 missing.

Indonesia was the hardest hit, with at least 126,000 people killed and more than 500,000 left homeless, mostly in Aceh province on Sumatra.

The region has since been hit by daily aftershocks that regularly cause people to flee their homes. On March 28, an 8.7-magnitude quake killed at least 647 people on Nias Island, which lies close to Padang.