A woman in labour was surely as surprised as the police who pulled over the car she was in to breath-test the male driver.

Two police officers were manning the random on-road booze station in West Melbourne on Wednesday night when a Toyota hatch-back pulled up at 6.15pm (AEST).

The Melbourne Highway Patrol officers approached the vehicle where they discovered a 35-year-old passenger giving birth in the front seat.

After paramedics were notified, the woman and her male partner, both from Werribee, were taken to St Vincent’s hospital.

The condition of the mother and baby is unknown at this stage.