The incident suspended services between Sunshine and Watergardens shortly after 4pm, in the lead up to commuter peak hour.

The line was reopened by about 4.40pm but Metro Trains was advising commuters of major delays of up to 30 minutes.

The 30-year-old female driver - the only occupant of the car - was treated at the scene for shock, a police spokesman said.

"Police will investigate the incident and assess whether any charges or penalty notices should be issued," he said.