Rescuers in Nepal are trying to reach hundreds of workers who have been trapped in tunnels since Wednesday's massive flash flood,  BBC reported. 

A controlled blast was carried out at a tunnel at the Trishuli site in the early hours of Monday. 

Nine hundred thirty three hydropower workers from sites across Nepal are missing - in total,  4,247 people are unaccounted for, with at least 903 known to have died, according to BBC. 

The number of missing is a sharp rise from 2,502, which was announced on Sunday. 

Of those missing, 3,655 are Nepali citizens, with 592 foreigners unaccounted for, BBC reported.