KATHMANDU, Nepal (AP) — Rescuers raced Monday to free hundreds of workers believed to be trapped in tunnels at hydropower sites that were buried in mud by catastrophic flooding on the Nepal-China border, as the death toll climbed and increasingly desperate families searched for missing loved ones.

The combined deaths in Nepal and China surpassed 900, with more than 4,700 people missing. A private-sector association representing power companies said at least 900 workers were unaccounted for at 12 hydropower projects damaged by the flash floods in Nepal’s Rasuwa and Nuwakot districts.

About 500 of those workers were believed to be trapped in tunnels. At least one expert said that some workers could have access to oxygen, but others warned that the chances of finding survivors were diminishing.

Some workers managed to call for help when the disaster struck last Wednesday, and others who managed to flee reported to authorities and relatives that many of their colleagues were still in the tunnels, said Mohan Kumar Dangi, president of the Independent Power Producers’ Association, Nepal, or IPPAN.

It was unclear whether rescuers have had any contact with the trapped workers since the initial calls for help.

Six days after the disaster, fears were growing that some might have suffocated, Dangi said.

Giant tunnels are built to control water flow
Rescue efforts were focused on people trapped in the gigantic tunnels built for controlling the flow of water.

“These tunnels are big enough to drive trucks through,” said Jakob Steiner, a geoscientist at the University of Graz in Austria based in Dhaka, Bangladesh. “And from what we understand, they have managed to get oxygen to some of those stuck inside and are trying to rescue them now. It’s a race for time, though, as people need food and water.”

In the Upper Trishuli-1 Hydropower Project, in the hard-hit Rasuwa district, at least 576 people were missing, Dangi said, adding that around 300 of them were believed to be trapped inside the project’s tunnel.

At the Trishuli-3 Hydropower Project, crews were working to descend about 15 meters (50 feet) into a tunnel in an effort to reach those believed trapped inside, according to Brig. Gen. Raja Ram Basnet, Nepal’s army spokesman.

Workers shoveling mud from a flood-ravaged power station in Dhading, Nepal, told The Associated Press that the station is a key connection for providing power to over 20,000 people in the region.

Chinese media highlight government efforts to rebuild roads
On the Chinese side, rescue and recovery efforts included rebuilding the road leading to the Gyirong Port border crossing that regulated travel between China and Nepal.

Although some rescue teams have managed to reach the border, that represented only a portion of the force.

Chinese state media coverage has focused largely on the official response, highlighting the deployment of firefighters, the People’s Liberation Army and instructions from top leaders. Little is known about victims on the Chinese side.

Families are desperate for information about missing loved ones
Nepal’s disaster agency said Monday that 903 deaths had been counted in that country, with 4,247 people missing, including 592 foreigners. As of Sunday, Chinese authorities reported 16 deaths and 546 missing. Chinese state media said 261 of the missing were foreigners, including over 100 Nepalis.

Two days after the disaster, Maraval Nagappan traveled to Nepal to search for his son, who was among the missing. He visited rescue centers and morgues and went as far as 40 kilometers (25 miles) from where his son was believed to have been, but found no sign of him.

His son, Sathya Narayan, had been leading a group of 49 Indian travelers who were returning from Mount Kailash — a sacred site in southwestern Tibet. The group has been missing since floodwaters swept through a Chinese immigration complex where they were waiting to cross into Nepal.

Nagappan, who owns the Chennai-based travel company that organized the pilgrimage, said the group had been expected to complete immigration formalities and leave for Nepal within about two hours. Instead of making the crossing, they were caught in the flood, Nagappan said.

The pilgrimage began Aug. 14. “I haven’t heard from my son since then. I don’t know whether he is alive or dead,” he told AP.

Surveillance footage showed water surging through the immigration complex at the border as people scrambled to escape. Nagappan said some of those seen fleeing were members of his son’s group and were identified by the clothes they were wearing.

Wednesday’s flash floods started after a glacial collapse high in the Himalayan region. Scientists who studied satellite images said bedrock underneath a glacier high in the Himalayan region had collapsed, taking part of the glacier with it. The rockfall was so extreme that it registered as a magnitude 5.2 seismic event.

The rocks and melted water then swelled the rivers in the valleys below, causing a torrent of water that swept buildings, bridges and earth downstream in Tibet and Nepal.