The group were driving down an empty road at around 9:30 pm in the Alzey-Worms area of the state, when for unknown reasons their BMW came off the road and hit two trees.
The impact left three women, aged 29, 33 and 39, and a 10-year-old boy dead. A 46-year-old man was taken to nearby Mainz university hospital with severe injuries. He is now fighting for his life, police said in a statement released during the night.
“The area is a disaster scene,” said police spokesman Gerd Fey.
Emergency service workers were at the scene of the crash until the early hours of Monday morning trying to clear the area, and the street has been blocked off.
An investigation is underway to figure out the cause of the accident.