The car lost control on a forest road on Prochenberg at Ybbsitz (in the district of Amstetten), and fell about 150 meters down a steep slope, said Philip Gutlederer of the "144 Emergency NE" team.
The alarm was raised on Sunday around 12 o'clock when a mountain rescue specialist discovered the vehicle.
When the rescue team arrived, it was already too late for the four occupants. The VW Golf is believed to have rolled over several times, causing severe injuries for the driver and his passengers.
The accident is likely to have taken place on Saturday afternoon around 3:30 p.m., according to the provincial fire commander. Police are continuing their enquiries to determine the cause of the accident.
According to the Salzburg Nachrichten newspaper, the four occupants from the nearby Amstetten were pensioners aged between 71 and 77 years.
The Prochenberg location is a "mountain" of Ybbsitz in Lower Austria, which at 1123 metres in height is a popular hiking destination.