AFP - At least 112 people were killed and hundreds remained missing in Indonesia after a tsunami triggered by a powerful earthquake smashed into a remote island chain, washing away entire villages.
Another 25 people have been killed after the eruption of the country's most active volcano, as the force of nature was unleashed in an area known as the Pacific "Ring of Fire".
The 7.7-magnitude quake struck late Monday in the Mentawai Islands off Sumatra generating waves as high as three metres (10 feet) that one official said had swept away 10 villages in one of the world's top surfing spots.
"At least 112 people were killed and 502 people have gone missing," West Sumatra disaster management head Harmensyah said Wednesday.
Less than 24 hours after the tsunami struck, Mount Merapi erupted on the island of Java, causing thousands to flee in panic as it spewed searing clouds of ash and claiming the lives of at least 25 people, including a baby.
"We heard three explosions around 6 pm (1100 GMT) spewing volcanic material as high as 1.5 kilometres (one mile) and sending heat clouds down the slopes," government volcanologist Surono told AFP.
Indonesia sits on a "ring of fire", where the meeting of continental plates causes high volcanic and seismic activity. The archipelago is frequently struck by powerful earthquakes and has the world's largest number of active volcanoes.
A 7.6-magnitude earthquake in September last year in Padang killed about 1,100 people while the 2004 Asian tsunami -- triggered by a 9.3-magnitude quake off Sumatra -- killed at least 168,000 people in Indonesia alone.
Health Ministry Crisis Centre head Mudjiharto said the Mentawai waves reached up to three metres high and waters swept as far as 600 metres inland on South Pagai island, the hardest hit.
Disaster Management Agency spokesman Agolo Suparto said 10 villages had been swept away.
Medical personnel were on their way to the worst-hit areas in helicopters but rescue efforts had been hampered by disruption to communications in the remote islands, which are about half a day's ferry ride away from Padang.
Disaster Management Agency aid coordinator Wisnu Wijaya told AFP that rescue teams from the capital Jakarta would join forces with local teams to evacuate bodies and deliver food aid, medicines, tents and blankets.
A group of Australian tourists reported that their boat with 15 people aboard was destroyed by a "wall of white water" crashing into a bay after the undersea quake and said some had to cling to trees to survive.
Rick Hallet, an Australian who operates a boat-chartering business in Sumatra, said a huge wave picked up another boat in the bay which smashed into his vessel, triggering an explosion and fireball.
"The bay we were in was several hundred metres across and the wall of white water was from one side to the other, it was quite scary," he told Fairfax Radio Network.
Another group of nine Australian surfers was alive and well after going missing following the quake and tsunami, officials said Wednesday.
Australia's foreign department said the nine on board the Southern Cross tour boat had lost mobile signal but contacted relatives late Tuesday, adding that they were not even aware of the tsunami pummelling the western islands.
US President Barack Obama, who lived in Indonesia as a boy and is due to return there on an Asian tour next month, pledged US help.
"(First Lady) Michelle and I are deeply saddened by the loss of life, injuries, and damage that have occurred as a result of the recent earthquake and tsunami in West Sumatra," he said.
"As a friend of Indonesia, the United States stands ready to help in any way."
Hundreds of kilometres away from the tsunami disaster zone, thousands of people fled in panic after the eruption of Mount Merapi, some covered in white ash, as officials with loudhailers tried to help them escape the area.
Search and rescue official Taufiq from Yogyakarta city told reporters that 12 bodies had been found in and around the house of the spiritual "gatekeeper" of the mountain.
"There are likely to be more victims as the terrain is difficult, roads are damaged and trees uprooted, it's dark and the condition of the volcano is still unstable," he said late Tuesday.
A local hospital doctor also said a baby had died from inhaling volcanic material.
The toll was updated to 25 on Wednesday morning.
Authorities had put an area 10 kilometres around the crater of Mount Merapi on red alert Monday, ordering 19,000 people to flee.
Volcanologist Surono said the latest activity at the 2,914-metre (9,616-foot) Merapi, was bigger than an eruption in 2006, which killed two people.
Its deadliest eruption occurred in 1930 when more than 1,300 people were killed. Heat clouds from another eruption in 1994 killed more than 60 people.