Tsunami survivors make their way past damaged houses Thursday after their village was hit by Monday's earthquake-triggered tsunami at Pagai island, West Sumatra, Indonesia.

MENTAWAI ISLANDS, Indonesia — Rescuers searching islands ravaged by a tsunami off western Indonesia raised the death toll to 343 today as more bodies were found and said the number is likely to climb higher because hundreds of missing people may have been swept away.

Elsewhere in Indonesia, the volcano that killed 33 people this week began erupting again, though there were no reports of new injuries or damage. Mourners held a mass burial today during a lull in Mount Merapi's rumblings.

President Susilo Bambang Yudhoyono was to meet today with survivors of the twin catastrophes, which struck within 24 hours in different corners of the seismically charged region, severely testing the nation's emergency response network.

Officials say a multimillion-dollar warning system installed after a monster 2004 quake and tsunami broke down one month ago because it was not being properly maintained.

In the tsunami-ravaged Mentawai islands, search and rescue teams — kept away for days by stormy seas and bad weather — found roads and beaches with swollen corpses lying on them, according to Harmensyah, head of the West Sumatra provincial disaster management center.

Some wore face masks as they wrapped corpses in black body bags on Pagai Utara, one of the four main islands in the Mentawai chain located between Sumatra and the Indian Ocean. Huge swaths of land were underwater and houses lay crumpled with tires and slabs of concrete piled on the surrounding sand.

Ferry Faisal, of the West Sumatra provincial disaster management agency, raised the official toll today to 343 from 311 earlier in the day. He said 338 people are still missing.

Harmensyah said the teams were losing hope of finding those missing since the wall of water, created by a 7.8-magnitude earthquake, crashed into the islands on Monday.

"They believe many, many of the bodies were swept to sea," he said.

Today, more than 100 survivors crowded into a makeshift medical center in the town of Sikakap on Pagai Utara. Some still wept for loved ones lost to the 10-foot wave as they lay on straw mats or sat on the floor, waiting for medics to treat injuries including broken limbs and cuts.

Hermansyah, a local fisheries ministry official who survived the earthquake and wave that hit Sikakap because he was on higher ground, quickly formed a rescue coordination committee and began traveling to other areas, finding several villages flattened.

"Not even the foundations of houses are standing. All of them are gone," said Hermansyah, who like many Indonesians uses a single name.

He said the devastation he saw indicates the wave could have been higher than reported in some areas — perhaps more than 20 feet high.

About 800 miles to the east in central Java, Mount Merapi began spewing hot clouds of ash again at around 4:30 p.m. today, according to the Indonesian vulcanology agency Subandriyo. Most residents have been evacuated from the area.