The tsunami and volcanic eruption in Indonesia have killed more than 300 people, with at least another 400 missing.
A 7.7-magnitude quake hit 78km west of South Pagai in the Mentawai Islands at 9.42pm on Monday local time.
The earthquake caused a tsunami that pounded islands in the remote Mentawai chain with waves up to three metres high.
Rescuers say 13 villages were washed away, but have yet to reach another 11 settlements they believe were also swept away.
The death toll from the tsunami has risen to 343 and at least 400 people remain missing on Thursday.
Disaster officials say clean water is scarce. Rescue teams and medical personnel are battling tough conditions and bad weather to reach the survivors and search for the missing.
Hundreds of workers from the military, police and the Disaster Management Agency are now on the scene.
Local television showed footage of villages flattened by the wave, with survivors combing through rubble for belongings.
Warning system 'vandalised'
Officials in Indonesia say an early warning system put in place after the deadly Indian Ocean tsunami six years ago was not working when the tsunami struck the western Mentawai islands.
One official says two devices in the sea that measure waves had been vandalised, the BBC reports.
Indonesian President Susilo Bambang Yudhoyono flew back from Hanoi, where he had been due to take part in a summit of Asian leaders, to oversee relief efforts for the Sumatra tsunami and the eruption of the Mt Merapi volcano.
Mt Merapi, one of Indonesia's most active volcanoes, spewed out clouds of ash and jets of searing gas in an eruption that has killed at least 29 people and injured 14.
The mountain first erupted on Tuesday. It is on the outskirts of the city of Yogyakarta on Java island.
Authorities have been battling to handle both disasters, with more than 40,000 villagers evacuated from the slopes of Mt Merapi, where many houses have been destroyed, their ruins lying covered in white ash.
A hospital official said it was likely that among the dead was the elderly spiritual guardian of the mountain, Mbah Maridjan, believed by many Javanese to possess magical powers.
Many of the victims had been found in or around Maridjan's house in the village of Kinahredjo, close to the volcano's crater, local media reported.
Some villagers are trying to return to their homes, despite the eruptions.
In a 1994 eruption after the volcano's lava dome collapsed, 70 people were killed. The volcano killed 1,300 people in 1930.
In December 2004, a tsunami caused by an earthquake of more than 9 magnitude off Sumatra killed more than 226,000 people.
It was the deadliest tsunami on record.