“I still have a 50% hope that he is alive because there is an oxygen system inside,” Sita Pandey, whose husband was working in the plant when the floods hit, told Nepalese daily Kantipur.

Nepal relies heavily on hydropower and has spent years developing the projects along its mountainous river systems. At least 11 projects either completed or under construction were damaged in the floods, authorities said.

Rescuers began pumping air into a tunnel over the weekend, but the families of those trapped say that should have been done earlier.

A team was able to get into a tunnel leading to one hydropower plant earlier on Monday, but withdrew after finding no one there.

“The longer it takes, the more our hope dies. This operation must move much faster because every second is meaningful to us,” Jiban Khadka, whose relative is also trapped inside the plant, told Kantipur.

“It’s a frustratingly slow operation,” Khadka added.

Nepalese leader Shah said rescue operations had been “intensified”, noting that 11,379 people had been rescued so far.

Another family member anxiously awaiting news is Priya Kharel, whose brother Milan was working as an engineer in the Upper Trishuli-1 plant when the floods hit.

“Those who returned from the hydropower site said there were people inside the tunnel,” she told BBC News Nepali. “So there is hope that if the army reaches them quickly, they can be saved.”