The death toll from a tsunami that hit the coast of Indonesia after a volcanic eruption rose above 370 on Monday, as rescuers dug through rubble with heavy machinery and bare hands along an expanding section of coastline affected by the deadly waves.

More than 120 people are still missing and more than 1,400 were injured when the tsunami struck the Indonesia islands of Java and Sumatra almost without warning late Saturday, shortly after the Anak Krakatau volcano erupted in the Sunda Strait dividing the islands.

Earlier Monday morning, Indonesia's Disaster Management Agency had put the death toll at 281. But the agency later said 373 people were confirmed dead, 1,459 injured and 128 missing.

Indonesia's Meteorology, Climatology and Geophysics Agency said Monday it had concluded that "the eruption triggered a landslide underwater" at Anak Krakatau.

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"The landslide was analysed, and the magnitude of the tremor was 3.4 from our analysis," the agency's head, Dwikorita Karnawati, told a news conference.

A man stands on the debris following a tsunami in Carita beach, Indonesia. Photo / AP
A man stands on the debris following a tsunami in Carita beach, Indonesia. Photo / AP

The disaster has raised fresh questions about the effectiveness of Indonesia's tsunami early-warning system, established after the Indian Ocean tsunami struck on Dec. 26, 2004, killing 226,000 people in 14 countries, including more than 120,000 in Indonesia, but since undermined by significant budget cuts.

"Our sensors can give early-warning signs based on tectonic quakes, because more than 90 percent of the tsunamis in Indonesia are caused by tectonic quakes," Karnawati said. "When our sensors go off, we can give a warning within a maximum of five minutes."

But Karnawati said no system was in place to monitor the oceanic impact of volcanic activity, and so the sensors gave no warnings. That is despite the fact that the vast Indonesian archipelago lies on the "Ring of Fire," an arc of volcanoes and fault lines in the Pacific Basin.

Sutopo Purwo Nugroho, a spokesman for Indonesia's Disaster Management Agency, tweeted that Indonesia has 127 volcanoes, 13 percent of the global total, including some at sea and on small islands. These volcanoes could cause a tsunami on eruption, meaning that such a system was needed, he said.

A network of ocean buoys that are supposed to warn of sudden rises in water levels was also not functioning on Dec. 22 in the Sunda Strait, he tweeted, blaming "vandalism, budget cuts and technical damage."

A man carries a usable item following a tsunami in Carita beach, Indonesia. Photo / AP
A man carries a usable item following a tsunami in Carita beach, Indonesia. Photo / AP

"The absence of an early warning system caused the tsunami potential to go undetected," he wrote. "No signs of an incoming tsunami were detected so people didn't have enough time to evacuate."

Problems with tsunami-detection buoys were also one of the factors blamed for the failure to properly anticipate an even more devastating tsunami that struck the Indonesian island of Sulawesi in September, killing at least 2,256 people.

And so on Saturday night, just over 20 minutes after the eruption, a wall of water 6 to 10 feet high hit the coastline of northwestern Java and southeastern Sumatra without warning, sweeping up everything in its path along the shoreline, including people, boats and cars.

More than 600 houses were destroyed, according to Indonesia's Disaster Management Agency. Many were ripped from their foundations, with the floodwaters carrying off large chunks of wood, metal and concrete.

Nine hotels along the coast were also damaged. Most of the victims were Indonesian citizens, including many enjoying a pre-Christmas beach getaway not far from the capital Jakarta, but foreigners were also visiting the area.

An excavator is used to clean up the debris following a tsunami in Carita beach, Indonesia. Photo / AP
An excavator is used to clean up the debris following a tsunami in Carita beach, Indonesia. Photo / AP

More than 5,360 people have fled to higher ground or been evacuated to temporary shelters in schools and other buildings. Authorities warned that continued volcanic activity and unusually high tides linked to a full moon meant that a second tsunami remained a possibility.

"Weather forecasts suggest extreme weather, including strong winds and torrential rain, which may trigger high tides and last until at least Wednesday," Karnawati said. "Residents should not panic, but please refrain from conducting any activities near beaches."

Abdul Mutolib, 53, was watching TV with his family when he heard shouting and saw his neighbours running around, bare-chested and wearing only sarongs.

"What happened?" he asked them. "Tsunami! Tsunami!" he said they replied.

His house, 300 yards from the coast, was not affected, but he has fled inland anyway to a cousin's house, where he is staying along two other families.

Nearby, a building usually used for Koranic studies houses more than 300 evacuees who are sleeping on thin mats. Women and children stay in the building while the men patrol outside, he said.

People inspect the wreckage of a car swept away by a tsunami in Carita, Indonesia. Photo / AP
People inspect the wreckage of a car swept away by a tsunami in Carita, Indonesia. Photo / AP

Indonesia's Search and Rescue Agency was joined by the military, police, medical teams and volunteers as aid trickled in to Pandeglang, the worst-affected area along Java's west coast, around about 60 miles from Jakarta.

The Indonesian Medical Association said it has sent doctors, medical supplies and equipment, adding that many of the injured require orthopedic surgery or neurosurgery.

Authorities said they deployed seven excavators and 12 dump trucks to sift through and remove the debris, but many rescuers simply used their bare hands to search for survivors. Trucks also brought in water and sanitation equipment.

Popular beach resorts were turned into ghost towns, with concrete, wood and debris from thatched bamboo huts strewn along the coast. Yellow, orange and black body bags were laid out, the Associated Press reported, as weeping relatives identified the dead.

Police officers rescued a 5-year-old boy on Sunday who had been trapped for nearly 12 hours in a car buried under fallen trees and rubble, according to a video posted by the police on Twitter. The military said it has deployed troops to distribute aid and blankets, as well as sending in medics.

A rescuer is seen through a damaged house as he takes part in a search operation. Photo / AP
A rescuer is seen through a damaged house as he takes part in a search operation. Photo / AP

President Joko Widodo, who is running for re election in April, also traveled to the area by helicopter Monday and said he had instructed the Meteorology, Climatology and Geophysics Agency to buy an early warning alert system.

The Energy and Mineral Resources Ministry's Center for Volcanology and Geological Hazard Mitigation said a tsunami caused by a partial collapse of a volcano was a rare event globally and was difficult to predict, but it nevertheless recommended a system of tidal stations, buoys and/or "visual monitoring with remote sensing" in the waters surrounding Anak Krakatau, Bloomberg News reported.

The tsunami also reached the southern tip of Sumatra, where at least 60 people were killed in the South Lampung region. Nugroho, the spokesman for the disaster agency, said two other districts or regencies on the southern end of Sumatra - Tanggamus and Pesawaran - were also affected by the tsunami.

Some roads were blocked with a combination of debris and traffic caused by the exodus, Reuters reported, although Salbiyah, an aid worker for Catholic Relief Services who uses only one name, said access to affected areas was generally good and food supplies adequate in villages she had visited around Pandeglang.

She said many fish storehouses were destroyed along the coast, but that houses made from stone were still standing.

Tsunami survivors sit at temporary shelter in Tanjung Lesung, Indonesia. Photo / AP
Tsunami survivors sit at temporary shelter in Tanjung Lesung, Indonesia. Photo / AP

There was so little warning that an Indonesia rock band, Seventeen, was swept from the stage just as it was beginning a song at a year-end party for a state-owned electricity company, held under a tent on the beach.

The group's bass player, guitarist, drummer and road manager were among those killed, while the lead singer's wife is missing. At least 29 employees and relatives from the electricity company in the audience also died.

"The tide rose to the surface and dragged all the people on site," the band said in a statement. "Unfortunately, when the current receded, our members were unable to save themselves while some did not find a place to hold on."

The tsunami added more deaths and misery to a year of tragedies and natural disasters in Indonesia, an archipelago of more than 17,000 islands and 260 million people. Apart from the Sulawesi tsunami, an earthquake killed 505 people on the island of Lombok in August, and a Lion Air plane plunged into the ocean in October, killing all 189 people on board.

Anak Krakatau had been spewing ash and lava for months, with plumes reaching hundreds of feet in the air in the weeks leading up to the tsunami.

Its deadly impact is a reminder of its historic past. The volcano's name means "Child of Krakatau," the island rising from the sea only in 1927, after one of the largest, most devastating eruptions in recorded history occurred at the original Krakatau volcano in 1883.

That eruption, which caused the original volcano to collapse into the sea, killed more than 36,000 people in far-reaching tsunamis and sent so much ash into the sky that global temperatures fell.