KATHMANDU, Nepal: Rescue teams in Nepal are concentrating their efforts on three hydropower project tunnels where dozens of workers are believed to be trapped, authorities said this week.

The search comes two weeks after a massive flood and mudslide struck the Himalayan country, killing hundreds of people and leaving thousands missing in Nepal and neighboring Tibet in China.

The disaster happened on August 26, when a glacier collapsed into a river along the Nepal-China border. The sudden rush of ice, rocks, mud and water swept through the area and badly damaged at least 11 hydropower projects. Debris buried the entrances to several tunnels, cutting off workers who may have been inside.

Dharma Raj Upreti, head of Nepal's disaster management authority, said rescuers were continuing to search for survivors, with tunnels now among their main targets.

"Our search operation is focused on finding survivors, including in tunnels. Our bigger focus is on the Chilime hydroelectric project, where we believe people are trapped, because there was a canteen, residency and arrangements for food," Upreti told Reuters.

Rescue teams are also concentrating on the tunnels of the Upper Trishuli 3A and 3B hydropower projects. The two projects are connected through an underground tunnel system, making the search particularly important.

Upreti said rescuers pumped oxygen into the tunnels through pipes to keep anyone trapped inside alive. Teams have also brought in new equipment that could help them clear debris and create an opening into the blocked tunnels.

In recent days, rescue workers have saved four people from different locations. A Chinese national was pulled alive from a tunnel on September 5. Rescuers rescued two hydropower workers from another tunnel a day earlier. A Nepali woman was also found alive after rescuers pulled her from the remains of her buried home the following day.

Despite these rescues, the disaster's scale remains enormous. At least 1,399 people have been confirmed dead in Nepal and Tibet, while more than 5,400 people are still missing.

The disaster has also caused heavy losses on the Chinese side of the border. As of September 5, at least 43 people had died in Tibet, and another 519 were reported missing.

China's state news agency Xinhua reported that none of the bodies recovered in Tibet so far belonged to foreign nationals.

Among those desperately searching for missing relatives is Australian medical student Sarada Viswanathan, 23. Her boyfriend, Rishab Iyer, and members of his family disappeared near the Nepal-China border after the glacier collapse triggered the massive flood of water and debris.

Viswanathan appealed to technology and telecommunications companies to share location and tracking information that could help rescue teams reduce the areas they need to search.

Viswanathan said Apple and Australian telecommunications company Optus had refused her requests for location data that might have helped establish the family's last known movements.

Optus said it could not comment on individual customers, while Apple did not immediately respond to requests for comment.

An earlier report said Life360 had also declined to discuss the specific case, but later clarified it had not.