A massive quake struck on Wednesday off the Indonesian island of Sumatra, a region devastated by the 2004 Indian Ocean quake and tsunami, but initial fears of another region-wide disaster faded as tsunami warnings were cancelled

Indonesian and Australian authorities called off their tsunami alerts within two hours of the 7.8 magnitude tremor, though it was still unclear if the quake had destroyed any buildings or killed people in Sumatra.

A National Search and Rescue Agency official gave an initial report of some deaths, but later withdrew those comments.

"Up until now, there is no information about deaths," said Heronimus Guru, the National Search and Rescue Agency's deputy head of operations. Guru earlier told Reuters the earthquake had killed some people, but that he did not know how many.

There were no immediate reports of damage, but the shallower a quake, the more dangerous it is.

The U.S. Geological Survey originally put the magnitude at 8.2, before lowering it to 7.8. The epicentre was 808 km southwest of Padang, USGS said. It was 10 km deep.

"So far there have been no reports (of damage)," Andi Eka Sakya, an official of the National Meteorological Agency, told TVOne. "In Bengkulu (on the southwestern 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 did not feel the quake.

Erwin, a resident of Mentawai, a chain of islands off Sumatra, told Metro TV: "I am at the beach currently looking to see any tsunami sign with my flashlight. There's nothing. A few minutes have passed but nothing, but many people have already evacuated to higher places."

Kompas TV said patients at hospitals in Padang were being evacuated from buildings. A TVOne reporter said Padang residents were panicking and there were heavy traffic jams.

Indonesia, especially Aceh, was badly hit by the Indian Ocean tsunami in 2004. A 9.15-magnitude quake opened a fault line deep beneath the ocean on Dec. 26, 2004, triggering a wave as high as 17.4 metres that crashed ashore in more than a dozen countries to wipe some communities off the map in seconds.

The disaster killed 126,741 people in Aceh alone. Indonesia 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.