A powerful undersea earthquake that struck off the Indonesian islands of Sumatra and Java has killed four people and damaged hundreds of buildings, the nation's disaster agency says.
Indonesia issued a tsunami warning within minutes of the 6.8-magnitude quake on Friday night. The warning lasted two hours and sent people living along the coast fleeing to higher ground.
The strong quake was felt in the capital Jakarta and people rushed out of high-rise buildings.
Thousands residents of Pasaran Island, Bandar Lampung fled to the Lampung Governor's office area, following the earthquake. Source: AAP
Four people died - some of heart attack or fatigue - as people rushed away from the coastline, disaster mitigation agency spokesman Agus Wibowo told a news briefing.
Four others were injured and more than 200 buildings were damaged by the quake, he said.
Many of the people who took to higher ground, including about 1000 taking shelter in the gubernatorial office in the Lampung province, had returned home, Wibowo said.
The US Geological Survey put the epicentre in the Indian Ocean about 227km from the city of Teluk Betung on Sumatra.
The location of the earthquake, which struck at a depth of 42.8 km near Tugu Hilir, Indonesia. Source: USGS
This lies along the Sunda fault, where researchers have long found a potential for a megathrust quake, Wibowo said, referring to a very large earthquake that occurs in a region where one of the earth's tectonic plates is thrust under another.
Wibowo warned that a study by Indonesia's geophysics agency showed there is a potential quake of 8.8 magnitude in the area that would trigger a 20-metre high tsunami, though he added that no one can predict when it would happen.
"People have to be alert, houses need structures that can withstand quakes," he said. His agency has also launched projects to educate people living along the coastline on how to respond to a tsunami threat, he said.
Indonesia is situated on the so-called Pacific Ring of Fire, which is frequently hit by earthquakes that are sometimes accompanied by tsunamis.
The most devastating in recent Indonesian history was on December 26 in 2004, when a magnitude 9.5 quake, which scientists have associated with a megathrust event.
That quake triggered a massive tsunami that killed around 226,000 people along the shorelines of the Indian Ocean, including more than 126,000 in Indonesia.
Last year, a tsunami hit the city of Palu in Sulawesi island, killing thousands, while a crater collapse at the Anak Krakatau volcano triggered a tsunami that killed at least 430 people in an area near the latest quake.
