A driver has died after a two-car crash on the Sydney Harbour Bridge which brought traffic to a standstill for more than an hour. 

Emergency services were called to the scene at 12.40pm on Saturday following reports of the incident.

A NSW Ambulance spokesperson told the Daily Mail the crash was potentially caused by a medical episode.

One of the drivers, a man in his 60s, was rushed to Royal North Shore Hospital in a critical condition, where he later died.

He is yet to be formally identified and a report will be prepared for the coroner.

An investigation into the circumstances surrounding the crash has been launched. 

Paramedics assessed four occupants of the second car and none of them required treatment.

Two of the four northbound lanes were closed and traffic remained at a standstill until shortly before 2pm. 

A driver is in a serious condition after a two-car crash on the Sydney Harbour Bridge, with traffic at a standstill for kilometres.

A NSW Ambulance spokesperson told the Daily Mail the incident was potentially caused by a medical episode

Live Traffic NSW said three of the four northbound lanes had been closed and lines of vehicles could be seen at a standstill

One of the four southbound lanes was also shut by officials while they cleared the road.

Drivers approaching the bridge were advised to reduce speed to 40km/h, prepare to merge and expect significant delays. 

Authorities have since urged motorists to continue exercising caution. 

As inquiries continue police are urging anyone with information about the incident – or was in the area at the time with any relevant dashcam or mobile phone footage – to contact Sydney City Police Area Command or Crime Stoppers on 1800 333 000.