LABUAN, Indonesia (Reuters) - The death toll from a tsunami triggered by a massive underwater landslide on an Indonesian volcano rose to 281 on Monday, as rescuers using heavy machinery and their bare hands searched through debris in the hope of finding survivors.

Indonesia's meteorological agency confirmed the collapse of part of Anak Krakatau, a volcano midway between Java and Sumatra, caused a tsunami 2-3 meters (6-10 feet) high that hit the rim of the Sunda Strait late on Saturday.

At least 1,000 people were injured and nearly 12,000 coastal residents forcibly evacuated to higher ground, with a high-tide warning extended to Wednesday.

Anak Krakatau, which means child of Krakatau, has been spewing ash and lava for months. Sixty-four hectares (0.64 square km) of the southwest side of the volcano collapsed.

"This caused an underwater landslide and eventually caused the tsunami," said Dwikorita Karnawati, head of the meteorological agency.

Aid trickled in to Pandeglang, the worst-affected area on Java's west coast, and hundreds of soldiers and volunteers picked through piles of wreckage looking for bodies along a 100 km (60 mile) stretch of beach.

The vast archipelago, which sits on the Pacific "Ring of Fire", has suffered its worst annual death toll from disasters in more than a decade. Earthquakes flattened parts of the tourist island of Lombok in July and August, and a double quake-and-tsunami killed more than 2,000 people on Sulawesi island in September.

Saturday's tsunami came with almost no warning and destroyed more than 700 buildings, from small shops and houses to villas and hotels.

Disaster mitigation agency spokesman Sutopo Purwo Nugroho said Indonesia had no warning system for volcanoes and underwater landslides.

President Joko Widodo visited the area on Monday and said an alert system was needed.

"I've instructed the Meteorology, Climatology, and Geophysical Agency to buy a detection device or a system that would provide an early warning so that the residents can be spared," he told reporters.

Several scientists said earlier the most likely cause of the tsunami was the collapse of part of the volcano.

Indonesia tsunami disaster zone: https://tmsnrt.rs/2RdjsMd

ROADS JAMMED

Families continued to stream out of the area on Monday for fear of further tsunamis, jamming roads already blocked by debris.

Britain, Australia and Canada advised nationals to monitor the situation closely and the United States embassy said it was ready to assist if needed.

The timing of the tsunami over the Christmas season evoked memories of the Indian Ocean tsunami triggered by an earthquake on Dec. 26, 2004, which killed 226,000 people in 14 countries, including more than 120,000 in Indonesia.

Witnesses recalled how a light breeze was followed by a huge wave that smashed together wooden fishing boats moored off the coast.

Dented vehicles were shunted together by a wave that carried chunks of metal, felled trees and left roof tiles, wooden beams and household items strewn across roads. Some cars ended up in rice fields.

Nurjana, 20, ran for half an hour to the mountains after the tsunami hit. Her beachside stall, where she sold snacks to tourists, was washed away.

"I opened the door straight away and saved myself. I jumped over the wall," she told Reuters.

"Everything is destroyed."

Heavy equipment was being used to help with rescue efforts. Medics were sent in with the military, while groups of police and soldiers reached remote areas.

One team of volunteers who worked on disasters in Lombok and Palu was looking for victims at Villa Stephanie, one of dozens of beachside retreats, where eight people were missing.

"It's difficult here because it's piled with debris," said West Jakarta Tagana chairman Muhammad Idris, who led the team.

"This year has been pretty busy. The disasters have been more severe," he said.

At least five bodies were found in that area on Monday. Military and other rescuers used an excavator to remove cars and debris, including piles of steel roofing tangled like spaghetti.

MASS BURIAL

The western coast of Banten province in Java, Indonesia's most populated island, was also badly hit and at least 60 people were killed in Lampung in southern Sumatra, the disaster agency said.