BANDUNG, Indonesia (AP) — Nineteen members of Indonesia’s elite marine force are among 42 people missing after being swept away or buried by a deadly weekend landslide that tore through a mountainside in West Java province, officials said Monday.

The marines were training in rugged terrain and heavy rainfall when Saturday’s predawn landslide swallowed their camp and some 34 houses in Pasir Langu village on the slopes of Mount Burangrang. A search operation has grown from 500 to 2,100 personnel using bare hands, water pumps, drones and excavators.

Seventeen people have been confirmed dead, National Disaster Management Agency spokesperson Abdul Muhari said.

Four marines were among the dead, navy Chief of Staff Adm. Muhammad Ali told reporters. They were part of a 23-member unit training for a long-duration border assignment on the Indonesia–Papua New Guinea frontier, he said. The rest are unaccounted for.

“Heavy rain over two nights triggered the slope failure that buried their training area,” Ali said. “Heavy machinery has struggled to reach the site, the access road is narrow and the ground remains unstable.”

Ade Dian Permana, who heads the local search and rescue office, told reporters that 42 people were missing.

“The ground is still very unstable and mixed with water, which limits how far our teams can safely move,” he said.

Rescuers were digging through tons of mud, rocks and uprooted trees in a landslide that stretched more than 2 kilometers (1.2 miles), said Yudhi Bramantyo, the operation director of the National Search and Rescue Agency. He said that in some places the mud reached up to 8 meters (26 feet).

Authorities halted search operations at nightfall because limited visibility and unstable soil posed risks to rescuers, Bramantyo said.

Seasonal rains and high tides from about October to April frequently cause flooding and landslides in Indonesia, an archipelago of more than 17,000 islands where millions of people live in mountainous areas or near fertile flood plains.