Three people were gravely injured after two cars collided and hit a block of flats, police said.
The incident happened on the London road in Bedford just before 4am.
The impact caused extensive damage to the building, leaving a hole in the wall of one resident's bedroom and damage to a neighbouring flat and stairwell, police said.
No residents were injured, but two of the people believed inside the cars were taken to hospital in a critical condition.
A third man, thought to be a pedestrian, was seriously injured, police said.
One man was arrested on suspicion of vehicle theft and is being held in custody.
Police are urging witnesses to come forward and want to trace anyone else involved in the collision, especially people seen running from the scene of the accident.
The building is owned by Bedfordshire Pilgrims Housing Association (bpha).
It has been evacuated and will be assessed by a structural engineer, police said.
A spokeswoman said: "The collision has caused extensive damage to the flats. One resident, who was in bed at the time, has had a hole knocked into his bedroom wall and there is a hole knocked in the neighbouring flat, and the stairwell has been damaged."