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 950, with more than 4,400 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. As the rescue efforts intensified, four bodies were recovered from three mud-filled tunnels, Nepal’s army said.