Earthquakes have struck off the north-east coast of the Indonesian island of Sumatra and the waters around it have been rocked by waves as large as 6m (20ft).
The massive quake – at 9.33am local time – is likely to have been followed by smaller ones over the coming hours, with several more following.
A nearby geological agency has issued a tsunami warning for the Indian Ocean rim.
There have been no reports of casualties.
What is the official statement?
“Based on data, we have classified it as a very strong earthquake. Tsunami warnings are already in effect for the coastline with the potential to reach South-East Asia including Indonesia,” the US Geological Survey (USGS) said.
It advised the public to keep a look out for any potential tsunami waves.
Officials in Palu on Sulawesi island in eastern Indonesia have said people on the city’s outer reaches have been evacuated.
“There’s been some movement in the air and earth and people are frightened,” a resident in Padang – a small, metropolitan city on Sulawesi which had been due to host the Asean ministerial meeting – told the BBC.
Reuters news agency, quoting the local government, said that as many as 500,000 people living around the low-lying coast of Sumatra were affected.
Frances Watson, a freelance journalist, was in Palu and watched a tsunami occur off the coast there.
“Witnesses say a wave of about six metres, totally inland, flew within 5m of the seafront and broke into three pieces,” she said.
Evacuation and communications outages mean it is not clear whether people who may have been killed live or survived, she said.
“But there are a lot of people on the beach and there are small fires. There are rumours of bodies floating past the coast.”
Ms Watson said many people had decided to stay at home, fearing aftershocks, even if the pre-dawn shakes stopped within an hour.
“The power is out, the phones are out, the internet is down.”
Indonesia was hit by a huge earthquake and the tsunami it unleashed in 2004. About 140,000 people died along the resort island of Bali, the islands of Lombok and Java, and in Sumatra.
Photographs and footage from Indonesia’s Twitter account, showing the devastating impact of an earlier earthquake, have posted images of the quake’s aftermath, with the surrounding sea spattered with debris and holes cut through the sea defences.
Smaller aftershocks have rumbled across the area.
Tweet by Indonesia’s Mines and Energy Ministry
9.40am tremors & waves of various sizes reported to us. Overreaction ?. Likely caused by addition of secondary earthquakes. There has been no loss of life or injuries reported. #Indonesia #IndonesiaDisaster https://t.co/G3Ix9YnU7M — Ministry of Energy & Mineral Resources (@MinEnergyGovt) December 3, 2017
Tsunami danger for Australia
Quakes have also struck off the south-eastern coast of Australia’s mainland, and there are fears the potential is there for further deadly tsunamis.
There have been no reports of casualties or damage.
But a tweet from the Australian Department of Foreign Affairs and Trade said that the National Tsunami Warning Centre had issued a warning for “hazardous tsunami waves of up to 15m [50ft] above the tide level”.
The bureau is warning people to consider leaving areas with the potential for damage, such as low-lying coastal areas and the west coast of Tasmania.
How are Indonesians reacting?
Part of the reason for the quake’s immediate impact on people in Indonesia is that a TV station broadcast a warning of tsunami waves in more than 20 different languages, including many languages spoken in Indonesia.
Some Indonesian army soldiers gathered to see how badly the quake was affecting the city of Padang, 140 km (90 miles) from Palu, reports Al Jazeera.
During a news conference, the chief of the police in central Sulawesi, Sugeng Sebayo, told reporters that residents were being warned to be on the alert for possible aftershocks.
#Sulawesi #IndonesiaDisaster 12:00 to 13:00 met ongoing evacuations in Tadahun hospital, western Sulawesi #Indonesia #SulawesiDisasterTV5 pic.twitter.com/Ao7tpqmpD7 — The Province of Sulawesi (@SulawicoriBurek) December 3, 2017