The incident occurred near Bhachau railway station under Ahmedabad division of Western Railway where a double line is being constructed by the Rail Vikas Nigam (RVNL) Limited.
The labourers were involved in the construction of the bridge as part of the double lining work when the newly-built retaining wall fell on four of them, police said.
While three workers died on the spot, the injured was taken to a local hospital, where his condition is said to be critical, they said.
