Rescuers raced to free around 35 Indian construction workers trapped in a tunnel, two days after the hydroelectric dam they were helping to build was swept away by a wall of water from a collapsed glacier that barrelled down a Himalayan river.

The workers were among 197 people who officials said were still unaccounted for as the death toll from the disaster - which also broke apart bridges, cut off villages and scarred tracts of mountain landscape - rose to 28.