A major 7.7-magnitude earthquake struck off the west coast of Indonesia on Monday, seismologists said, causing localised waves in the remote area.

A tsunami warning was issued, and while it was later withdrawn and no casualties were confirmed, a group of Australian visitors reported that their boat was destroyed by a "wall of white water" crashing into a bay.

The undersea quake hit Indonesia's Kepulauan Mentawai region at 9.42 pm (1442 GMT) at a shallow depth of 20.6 km (12.8 miles), the US Geological Survey said.
The Mentawai Islands, 240 km west of Bengkulu on Sumatra island and 280 km south of Padang, are popular with tourists.

Rick Hallet, an Australian who operates a boat-chartering business in Sumatra, had 15 people on board his vessel in a bay off the islands when the quake struck.
"We felt a bit of a shake underneath the boat... Then within several minutes we heard an almighty roar... I immediately thought of a tsunami and looked out to sea and that's when we saw the wall of white water coming at us," he said.

"The bay we were in was several hundred metres across and the wall of white water was from one side to the other, it was quite scary," he told Fairfax Radio Network.
Another boat was anchored next to them, he said.

"The wave picked that boat up and brought it towards us and ran straight into us and our boat exploded, caught on fire, we had a fireball on the back deck and right through the saloon within seconds.

"I ordered everyone up to the top deck to get as high as possible, then the boat exploded and we had to abandon ship," he told Australia's Nine Network.

The group jumped into the water, some of them being swept 200 metres inland, and took shelter by climbing trees, waiting for 20 minutes to half an hour until the surges passed.

Eventually all the group, nine of whom were Australian, were accounted for, he said. The 7.7 earthquake was followed by powerful magnitude 6.1 and 6.2 aftershocks about five and eight hours later in the same area.

Residents reported shaking as far away as the West Sumatran provincial capital of Padang relating to the earlier quake, but fears of widespread damage eased a few hours later.

"There was shaking that went on for about three seconds or so. Residents panicked and ran to the hills but now they are starting to come down. There's no report of casualties or damage," Disaster Management Agency spokesman Priyadi Kardono told AFP.

The Indonesian Geophysics and Meteorology agency lifted an earlier tsunami warning. The power and shallow depth of the earthquake prompted the US-based Pacific Tsunami Warning Centre to issue a "tsunami watch" bulletin to guide local authorities on how to respond but that was later cancelled.

Indonesia sits on the Pacific "Ring of Fire," where the meeting of continental plates causes high volcanic and seismic activity, and the archipelago is frequently struck by powerful earthquakes.

A 7.1-magnitude quake off the north coast of Papua in June killed 17 people and left thousands homeless. The 2004 Asian tsunami — triggered by a 9.3-magnitude quake off Sumatra — killed at least 168,000 people in Indonesia alone. A 7.6-magnitude quake killed about 1,000 people in the port of Padang on September 30, 2009.