KATHMANDU, Nepal (AP) — Drone pilot Manish Maharjan has helped rescue teams in Nepal find people missing after last week’s catastrophic floods, sometimes using speakers mounted on the devices to call out to or play music for those stranded on hillsides.

But the search for hundreds of workers believed to be trapped in power plant tunnels — now a major focus of rescue operations — presents an entirely different challenge, he said.

“We found tunnels were filled with mud like toothpaste in a tube,” Maharjan said. “There was no hollow or empty space inside.”

Maharjan, who is also a filmmaker, joined the Nepal Army’s rescue efforts a day after the Aug. 26 flash floods, which have killed more than 1,000 people and left thousands missing in Nepal and Tibet.

“We used microphone speakers to call out to them. In some places, we even played songs and then waited for a response,” Maharjan said. “That worked in a few cases and helped us locate people.”