The Ministry of Manpower says the accident occurred Monday on an oil exploration rig being built by Jurong Shipyard Pte. Ltd.
The rig consists of a platform on three legs that can be raised or lowered. A shipyard spokeswoman says one of the legs failed to operate when workers were testing the rig, causing it to tilt to one side.
The ministry says the injured workers were taken to hospitals and 80 were later discharged. Three remained in an emergency ward.
An investigation of the accident is continuing.
Jurong Shipyard is a subsidiary of offshore engineering group Sembcorp Marine Ltd.