Police suspect that the accident was caused by two drivers racing each other. A third vehicle fled the scene, but the driver later called the police.
The accident occurred at 6.30pm on a country road between Västerås and Hallstahammar.
The driver of a Saab and a family travelling in an Opel were all seriously injured in the crash.
“The driver who was alone in his car skidded at high speed, came over to the wrong side of the road and collided with the Opel,” said police spokesman Ulf Palm.
Inside the Opel were two adults and three small children. After the crash the two adults were trapped inside the vehicle.
“One was very badly stuck and it took around 40 minute before we got that person out,” said Folke Åkerblom from Mälardalen Fire and Rescue Association.
Al of those involved in the crash live in Hallstahammar.
Several witnesses have told police that the Saab was racing with another car before the accident. The third driver made contact with police having first left the scene of the crash.
“He called himself and wanted to talk to a police office,” said Ulf Palm.
Police are waiting to question the Saab’s driver before deciding whether to press charges.