MENTAWAI ISLANDS, Indonesia — Rescuers searching islands ravaged by a tsunami off western Indonesia raised the death toll to 370 Thursday as more corpses were wrapped in body bags or buried by neighbors. Officials said hundreds of missing people may have been swept out to sea.

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

The twin catastrophes struck within 24 hours in different corners of the seismically charged region, severely testing the nation’s emergency response network.

Islanders dug graves and slung up tarps to sleep under in one of the areas hardest hit by a 10-foot wave that swept houses off their foundations and deposited the shattered remains in the jungle. Many residents who fled to the hills were refusing to return home for fear the sea might lash out again.

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. A German official at the project disputed that, saying the system was working but the quake’s epicenter was too close to the Mentawai islands for residents to get the warning before the killer wave hit.

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.

Agus Zaenal, of the West Sumatra provincial disaster management agency, raised the official toll Thursday to 370, up from 343 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, triggered by a 7.7-magnitute earthquake, crashed into the islands on Monday.

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

In a rare bright spot, an 18-month-old baby was found alive in a clump of trees on Pagai Selatan island on Wednesday. Relief coordinator Hermansyah said a 10-year-old boy found the toddler and that both his parents were dead.

On Pagai Seatandug island, the wave deposited giant chunks of coral and rocks the size of people into the places where homes once stood in Pro Rogat village, one of the hardest-hit areas with 65 dead. Villagers huddled under tarps in the rain and talked about how many who had fled to the hills were too afraid to return home.

Mud and palm fronds covered the body of the village’s pastor, 60-year-old Simorangkir. His corpse lay on the ground, partially zipped into a body bag. Police and relatives took turns pushing a shovel through the sodden dirt next to him to create his final resting place.

His grandson, Rio, 28, traveled by boat to Pro Rogat from his home on a nearby island to check on his relatives after the quake. He said he was picking through the wreckage when someone cried out that he had found a body. Rio walked over and saw his grandfather’s corpse partially buried under several toppled palm trees.

"Everybody here is so sad," Rio said, as family members prepared to place his grandfather in the grave.

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

Fisherman Joni Sageru, 30, recalled being jolted awake by the quake and running outside to hear screams to run to higher ground on his island of Pagai Selaton.

"First, we saw sea water recede far away, then when it returned, it was like a big wall running toward our village," Sageru said. "Suddenly trees, houses and all things in the village were sucked into the sea and nothing was left."

Officials questioned whether the tsunami warning system had functioned properly. The chief of Indonesia’s Meteorology and Geophysic Agency, Fauzi, said the special buoys that detect sudden changes in water level broke down last month because of inexperienced operators and poor maintenance.

However, Joern Lauterjung, head of the German-Indonesia Tsunami Early Warning Project for the Potsdam-based GeoForschungs Zentrum, said a warning did go out five minutes after the quake — but the tsunami hit so fast no one was warned in time.

"The early warning system worked very well — it can be verified," he said.

He added that only one sensor of 300 had not been working, and had no effect on the system’s operation.

About 800 miles to the east of the tsunami zone, Mount Merapi in central Java began spewing hot clouds of ash again at around 4:30 p.m. Thursday, according to the Indonesian volcanology agency Subandriyo.

Most residents have been evacuated from the area. It was unclear whether the new activity was a sign of another major blast to come. Tuesday’s eruption killed at least 33 people and injured 17, said Agustinus, a doctor at the local health department.

Residents from the hardest-hit villages of Kinahrejo, Ngrangkah, and Kaliadem — which were decimated in Tuesday’s blast — crammed into refugee camps. Officials brought surviving cows, buffalo and goats down the mountain so that villagers wouldn’t try to go home to check on their livestock.

Thousands attended a mass burial for 26 of the victims six miles from the mountain’s base. They included family and friends, who wept and hugged one another as bodies were lowered into the grave in rows.

Among the dead was a revered elder who had refused to leave his ceremonial post as caretaker of the mountain’s spirits. He was buried in a separate funeral Thursday.

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Associated Press writers Achmad Ibrahim in the Mentawai islands, Slamet Riyadi at Mount Merapi and Irwan Firdaus in Jakarta contributed to this report.