A portion of an under-construction tunnel between Silkyara and Dandalgaon on the Brahmakhal-Yamunotri National Highway collapsed early on Sunday, trapping around 40 workers inside, officials here said.

Personnel from the National Disaster Response Force (NDRF), State Disaster Response Force (SDRF) and police launched a search and rescue operation immediately after being informed of the accident, Superintendent of Police (Uttarkashi) Arpan Yaduvanshi said.