The incident took place when labourers were trying to water the flyover under construction to strengthen it, the police said.
The injured labourers were admitted to the government-run M Y Hospital, the police said.
Meanwhile, the Public Works Department's bridge division's executive engineer R N Mishra claimed that the incident took place because a speeding truck hit the supporting iron beam due to which the nearly 30-metre long portion of the flyover under construction collapsed.
