A powerful earthquake and several aftershocks have struck off the western Indonesian island of Sumatra, sparking fears of a tsunami.
Some buildings collapsed in West Sumatra after the quake hit
Tsunami alerts were issued for several nations in the Indian Ocean, though some have now been lifted.
Buildings collapsed on the west coast of Sumatra. Hospitals are on alert in case there are significant casualties.
A massive undersea earthquake sparked a tsunami that killed more than 220,000 people in December 2004.
The Pacific Tsunami Warning Centre issued an alert for the entire Indian Ocean region following Wednesday's main quake, which the US Geological Survey said measured 8.4.
Besides Indonesia, India, Sri Lanka, Malaysia and a number of small islands were put on alert. Kenya, on the western rim of the ocean, also raised the alarm.
There were unconfirmed reports of a small tsunami - estimated at 1-3m (3-10ft) hitting the Sumatran coast - but not causing major damage.
But about two hours after the quake, Indonesia's meteorology agency said the danger of a serious tsunami had passed, and Sri Lanka and India also dropped their alerts.
Wednesday's main earthquake struck at 1810 (1110 GMT), about 30km (18 miles) under the sea, some 130km (80 miles) south-west of the city of Bengkulu, the US Geological Survey said.
Local media said buildings had collapsed in Padang, the capital of the province of West Sumatra, and in the town of Mukomuko.
There were also reports of inhabitants fleeing swaying buildings in the capital Jakarta, 600km (370 miles) away, and in Singapore.
"You could see the road as if it was waving, people could hardly walk so they just lay flat on the road. I could also feel the earth I was standing on was like the sea," Zulkifli Lubis, a local journalist in Bengkulu, told the BBC.
Officials said it was very difficult to get clear communications with the area to make damage assessments.
They are sending disaster teams from the capital Jakarta, fearing that there may be significant casualties, says the BBC's Lucy Williamson in Jakarta.
Officials said at least two people had died and dozens were injured.
But as it is dark, and many of the stricken areas are be remote, it may take some time to find out how bad the situation is.
"At least one person died when he was hit by a falling tree when they were evacuating after the quake," Salamun Haris, an official from North Bengkulu district, told ElShinta radio.
"Dozens of people were injured in damaged buildings" across the district, he said, and hospitals were clearing wards in anticipation of receiving casualties.
This was one of the most powerful earthquakes in Indonesia since the one which caused the Asian tsunami in 2004.
That measured 8.9 and struck under the sea near the northern Sumatran province of Aceh, triggering a tsunami that killed more than 220,000 people around the rim of the Indian Ocean.
Our correspondent says quakes on this scale are rare and memories of 2004 have made the country terrified of a repeat.
Indonesia, part of the seismically active Pacific "Ring of Fire", is frequently shaken by earth tremors.