Harbour tunnel reopens after critical police pursuit

A man is in a critical condition and southbound lanes of the Sydney Harbour Tunnel have only now reopened after a motorcycle crash following a police pursuit.

The rider is in a critical condition and traffic remained backed up to the Lane Cove Tunnel as commuters attempted to make it home after extensive delays.

At 1.45pm Highway officers began a pursuit of the motorcycle, reportedly speeding on the Warringah Freeway, north of Sydney.

The rider of the motorcycle failed to stop and entered the tunnel where it is believed to have crashed into the rear of another vehicle travelling south. 

Six ambulance vehicles were required on scene.

The male rider was treated at the scene and was transported to St Vincent's Hospital where he remains in a critical condition.

The driver of the vehicle he hit was not injured.

A critical incident report is being completed by the Major Crash Unit.

Diversions were in place up until 6.30pm directing southbound traffic onto the Harbour Bridge.

There were initial reports southbound lanes would remian closed until 8pm tonight but they have since reopened, easing the heavy traffic congestion.

This is the second Sydney accident involving a police pursuit this week.

On Wednesday morning, 68-year-old Gai Vieira's vehicle was struck by a police car on the Kingsway in Cronulla, south of Sydney.

She was travelling with her young grandson when the police car t-boned her Mercedes while beginning a pursuit of another vehicle.

Ms Vieira remains in a serious condition and an investigation is underway to determine if the police vehicle involved had its lights and sirens activated at the time of the incident.