The 37-year-old woman who crashed a van on the Sydney Harbour Bridge on Wednesday morning, causing traffic to gridlock for kilometres, reportedly told police she smoked cannabis before getting behind the wheel.

Police have blamed drugs and fatigue as the major factors involved in the accident, according to News Corp .

The crash reportedly happened after the woman, who was driving a rented van full of suitcases, fell asleep and drifted into oncoming traffic.

Investigators were unable to test her at the crash scene because of her injuries but a blood sample was taken after she was transported by ambulance to a nearby hospital.

A police officer told News Corp the results of the blood test will be known within three to six week and no charges will be laid until then.