Uttarkashi District Magistrate Shridhar Babu Addanki told over phone that the mishap occurred at about 11.30 am in Sangamchatti area of Assiganga valley when a part of the bridge caved in all of a sudden, killing one labourer on the spot and injuring three others.
The injured have been admitted to the government hospital Uttarkashi, he said, adding that all the labourers were from West Bengal.
The 70-metre bridge was being built over Assiganga, a tributary of the Ganga, by the National Building and Construction Corporation.