A Ford Falcon sedan crashed into a power pole on the Great Western Highway between Bennett Road and Sydney Street at about 3.15pm.

A 17-year-old male died at the scene. A 19-year-old man from Dean Park and a 15-year-old Bidwill girl died later in hospital.

Two girls, aged 16 and 17, were injured in the accident and are still in hospital.

Police closed eastbound lanes between Sydney Street and Bennett Road for several hours.

St Marys police commander Ray Filewood said yesterday that police would investigate all possible causes of the crash.

''Today’s events are a poignant reminder to all drivers to adjust the way they are driving to the prevailing weather conditions,'' Superintendent Filewood said.

''Personal responsibility is just as important as sticking to the road rules.''

He appealed for anyone who might have seen a black Ford sedan on the highway before the accident to contact St Marys police on 9677 7499 or Crime Stoppers on 1800 333 000.