JAKARTA, Mar 3 — A powerful 6.4-magnitude undersea earthquake struck western Indonesia today, the US Geological Survey said, but there was no tsunami alert and no immediate reports of casualties or damage.

The quake hit at a depth of 37 kilometres (23 miles) at 5:37 pm (1037 GMT) close to Pulau Siberut, part of the Mentawai Islands, off the west coast of vast Sumatra island, said the USGS.

An official from Indonesia’s meteorological, geophysics and climatology agency Benny, who like many Indonesians goes by one name, said that there was no potential for a tsunami.

The quake was felt in several cities in West Sumatra province, including the provincial capital Padang, but there were no reports of damage, he said.

Indonesia sits on the Pacific “Ring of Fire” where continental plates collide, causing frequent seismic and volcanic activity.

A huge undersea quake in 2004 triggered a tsunami that killed more than 170,000 people in Aceh province, on western Sumatra island, and tens of thousands more in other countries with coasts on the Indian Ocean.