An undersea earthquake off Indonesia's Aceh province has killed at least 24 people, with dozens feared trapped in rubble, authorities said.

The 6.4 magnitude quake struck near the town of Sigli on Sumatra island where dozens of buildings have collapsed.

Indonesia's meteorological agency said there was no risk of a tsunami.

In 2004, Aceh was devastated by a tsunami caused by a massive undersea earthquake that killed 120,000 people in the province.

The US Geological Survey said the earthquake struck just offshore at 05:03 local time (22:03 GMT Tuesday) at a depth of 17.2km (11 miles).

Said Mulyadi, deputy district chief of Pidie Jaya, the region hit hardest by the quake, told the BBC that he is worried the number of dead could rise.

Local authorities say heavy equipment is being used to search for survivors.

The quake also shook the nearby provincial capital of Banda Aceh and prompted many people to flee their homes and workplaces across the region.

The island of Sumatra has been hit by several earthquakes this year.

Indonesia is prone to earthquakes because it lies on the notorious Ring of Fire - the line of frequent quakes and volcanic eruptions that circles virtually the entire Pacific rim.