Hundreds of buildings were damaged by the tremors
Fresh earthquakes have hit the Indonesian island of Sumatra, a day after the world's strongest tremor so far this year caused extensive damage.
At least nine people are known to have died in the earthquakes. But the full scale of the impact has yet to emerge.
Tsunami warnings were repeatedly issued and lifted, as many people ran inland fearing a repeat of the 2004 tsunami.
The largest tremor, of magnitude 8.4, has been followed by one of 7.8 and another of 6.4.
On Thursday, the authorities issued - and lifted - another tsunami warning following the 6.4-magnitude quake off the northern tip of the island of Sulawesi.
The earlier magnitude-7.8 quake struck Sumatra at 0649 on Thursday (2349 GMT on Wednesday), about 10km (six miles) under the sea, some 185km (115 miles) south-east of the city of Padang, the US Geological Survey says.
It came some 12 hours after the main tremor, about 30km (18 miles) under the sea, 130km (80 miles) south-west of the city of Bengkulu.
At least 40 people have been injured and hundreds of buildings damaged, officials say.
"Many buildings collapsed after this morning's [Thursday's] quake. We're still trying to find out about victims," Padang Mayor Fauzi Bahar told a local radio station.
In one village, 85% of about 1,000 houses were damaged, some badly, the BBC's Lucy Williamson in the area reports.
But no-one appears to have been killed in the village, our correspondent says.
Casualties appear to be lower than first feared, but officials warn that bad communications may be masking the scale of the impact.
Health officials in the capital, Jakarta, say teams carrying food and medicine are travelling to the area, and President Susilo Bambang Yudhoyono has ordered the army and police to assist.
The United Nations said its teams were also heading for Sumatra.
Wednesday's quake sparked warnings across the Indian Ocean, but only a small wave surge of about 1m (3ft) hit Sumatra, causing little damage.
But about two hours after the quake, Indonesia's meteorology agency said the danger of a serious tsunami had passed. India and Sri Lanka also called off tsunami warnings.
Thousands of people were reported to have spent the night sleeping in the open air in the areas of Bengkulu and Padang after the previous quake left them terrified.
Wednesday's earthquake was one of the most powerful in Indonesia since the tremor that 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.
Indonesia, part of the seismically active Pacific "Ring of Fire", is frequently shaken by earth tremors.
WHERE THE EARTHQUAKES HIT
Two earthquakes in same area, south-east of Padang, Sumatra
First earthquake at 1810 (1110 GMT) on Wednesday, magnitude 8.4
Second earthquake at 0649 on Thursday (2349 GMT on Wednesday), magnitude 7.8
Third earthquake of magnitude 6.4 at 1748 (0948 GMT) on Thursday, off northern Sulawesi