Police are appealing for information after a crash in St Clair last night.
About 10.30pm, emergency services were called to the M4 Motorway between Roper and Bennet Roads, St Clair, after reports a man was found unresponsive after a crash.
Officers attached to Nepean Police Area Command attended and were told a white Holden Commodore was seen swerving between lanes before it crashed into a retaining wall.
The driver was treated at the scene by NSW Ambulance paramedics and taken to Westmead Hospital in a serious condition.
It is believed the man may have suffered a medical episode.
As inquiries continue, police would like to speak with anyone who may have been travelling along the M4 Motorway, shortly before the incident.
Any witnesses or those who have dashcam vision from the area at the time are urged to contact Crime Stoppers on 1800 333 000.