JAKARTA: A powerful and shallow earthquake of magnitude 7.9 struck off the west coast of the Indonesian island of Sumatra on Wednesday, the US Geological Survey said, following which the government issued a tsunami warning for West Sumatra, North Sumatra and Aceh.

The epicentre was 808 kilometres southwest of Padang, USGS said. It was 10 km deep.

There were no immediate reports of damage or casualties but the shallower a quake, the more likely it is to cause damage. USGS originally put the magnitude at 8.2, and then 8.1, before lowering it to 7.9.

“So far there have been no reports (of damage) yet,” Andi Eka Sakya, an official of the National Meteorological Agency, told TVOne. “In Bengkulu (on southwest coast of Sumatra) they didn't feel it at all.”

President Joko Widodo was staying overnight at a hotel in Medan in North Sumatra and was safe, palace officials said. A Medan resident said he didn't feel the quake.

Indonesia, especially Aceh, was badly hit by the Indian Ocean tsunami in 2004.

The country 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.

Australia's Bureau of Meteorology issued a marine warning for distant Cocos and Christmas islands.

It did not advise evacuations, but said strong and dangerous currents were possible and people should secure boats and avoid waterfront areas. The warning noted that a tsunami had not been confirmed.