An expectant mother's fear - a baby boy's been born on Auckland's Southern Motorway this morning.

The New Zealand Transport Agency says at 9.30 a car heading to the city pulled over in the far left lane on the motorway just after Market Road.

A spokeswoman says someone in the car called emergency services to report a woman was in labour.

She says staff at the transport operations centre guided an ambulance to the scene and police blocked off the lane to create a safe work area.

A baby boy was delivered 15 minutes later.

Mother and baby are both doing well and have now left the scene.

It's believed they were taken to Auckland City Hospital.

The baby boy has been called Ivan.