Rescuers were scrambling Monday to reach workers who are believed to be trapped inside tunnels at hydropower sites buried in mud after flooding in Nepal and China. 

The combined deaths in the two countries are estimated to be over 900 people, with nearly 5000 people missing, the Associated Press reported. 

Of those 5,000 missing, at least 900 of them are workers who have been unaccounted for at 12 hydropower projects impacted by the floods. Mohan Kumar Dangi, president of the Independent Power Producers’ Association, Nepal, said approximately 500 of the 900 missing workers are trapped in the tunnels at the sites. 

One expert told the Associated Press that the tunnels offer enough space for people to take refuge and some could have access to oxygen. Other experts said the chances of finding survivors are falling.