A tsunami warning was briefly triggered in Indonesia, off the island of Sumatra, after a 7.3 magnitude earthquake [Source: TheGuardian]

Indonesian authorities urged caution as residents returned gradually to their homes in western Sumatra after being rattled by a magnitude 7.3 earthquake and several aftershocks.

The earthquake, which took place out at sea at about 3 a.m. (2000 GMT Monday), triggered a tsunami warning that was lifted two hours later. There were no reports of casualties.

Residents in Padang, a city on the west coast of Sumatra, said they had panicked as tsunami warning sirens wailed and forced evacuation to higher ground in the middle of the night.

“We just ran because we heard there was a tsunami. I just brought my family, we didn’t bring anything else,” Hendra, a Padang resident who goes by one name, said while in an evacuation zone.

Indonesia experiences frequent earthquakes because it straddles the so-called Pacific Ring of Fire, a seismically active zone where different plates of the earth’s crust meet.

The national disaster mitigation agency urged residents to stay alert and ensure that home exits remained unblocked in case people needed to rush outside again.

“Especially for people living in coastal areas, if there is an earthquake that lasts more than 30 seconds, please immediately go to a higher place to anticipate the possibility of a tsunami,” it said in a statement.

The agency said there were power outages in some parts of the Mentawai Islands, which were closest to the epicentre.

Several aftershocks were recorded and a tide gauge at Tana Bala island off the western Sumatra coast recorded an 11-centimetre rise in water levels after the main quake, it added.

Padang and West Sumatra province were struck by a magnitude 7.6 earthquake in 2009 that killed more than 1,100 people, injured many more and caused widespread destruction.