A 19-year-old woman is dead after a one-car crash on State Highway 20 in Auckland early today, and police say they are working hard to figure out the circumstances of her death.

Police said a 20-year-old man is helping with their enquiries after the incident, which occurred at 3.20am.

A police spokesperson said they were advised the car had crashed, and located the deceased woman at the scene. An earlier press release described it as a “serious incident” and said one person had been arrested.

The scene of the incident on the southwestern motorway this morning. Photo / Hayden Woodward

The road has been closed at the Puhinui and SH20B onramp and also the Roscommon Road and Cavendish Drive onramp, meaning travel to Auckland Airport will be disrupted.

Anyone travelling to the airport should detour Papatoetoe and SH20A. The road is expected to be closed for some time while police complete a scene investigation.

A witness said the vehicle involved was facing the wrong way on the South Western Motorway.

Police investigate the scene of a fatal crash this morning. Photo / Hayden Woodward

”A team of police staff including Serious Crash Unit, Photography and Detectives were at the scene, and the vehicle had moderate damage to the front. The boot was also open.”

Motorists are advised to avoid the area and take alternative routes where possible.

Police said they realised “the road closure will cause disruption and officers are working hard to complete the scene examination as quickly as possible so the road can be reopened”.