POLICE are conducting investigations into what caused three cars to crash in the Royal National Park on Saturday night.

About 11:25pm three cars were travelling east along Sir Betram Stevens Drive and navigating a sharp bend when they all lost control, left the road and crashed into trees.

Police and paramedics attended the scene and the driver and passenger from one of the vehicles were taken by ambulance to St George Hospital for treatment of minor injuries.

The road was closed for more than three hours while all three vehicles were removed from the scene and examinations of the area conducted.

Sutherland Police are investigating what caused the crashes and believe up to 40 litres of oil had been deliberately poured over a 100m stretch of the road near Warumbul Road.

Sir Betram Stevens Drive has now been cleaned with a large amount of sand used to soak up the oil, however, police are warning motorists that the surface may still remain slippery and to exercise caution.

Meanwhile earlier in the night Wollongong police were called to Keiraville where a child had been locked in a car.

Paramadics were first called to Gipps Road about 9am after a triple zero call. The child had been locked in a car for more than 15 minutes in a parking area outside a set of shops. The child was treated for heat exposure at the scene but did not require transport to hospital.

Police are investigating.