An earthquake measuring 6.4 magnitude struck off the Indonesian island of Sumatra on Tuesday, the US Geological Survey said, but there were no reports of damage or casualties.

The quake was 37 km (23 miles) deep and centred 179 km (111 miles) offshore. It was felt by people on land but there was no panic, Indonesia's disaster agency said. There was no word on a tsunami.

Indonesia, badly hit by the Indian Ocean tsunami in 2004, straddles the so-called Pacific Ring of Fire, a highly seismically active zone where different plates on the earth's crust meet and create a large number of earthquakes and volcanoes. – Reuters