Two teenagers, a boy and a girl, are among three people killed in a crash involving a school coach on the A66 near Keswick in Cumbria.
The driver of a Honda Civic also died in the crash, at about 1545 BST. Four people are in a critical condition.
The Keswick High School coach was carrying pupils aged 11 to 18. It is believed to have swerved and overturned near Bassenthwaite Lake.
Six helicopters, police, fire and ambulance crews attended the scene.
A Red Cross support centre was set up at Braithwaite School to offer first aid and emotional support.
About 35 other people were injured in the collision.
Ch Insp Kevin Greenhow of Cumbria Police said: "My officers and people from the other emergency services found a very difficult situation to deal with.
"There were people who have been seriously injured, that was obvious from the outset, and also people suffering from the traumatic effects of what has happened.
"It will have been difficult, but they know what they have to do in their role and that's what they will have been doing."
Casualties have been airlifted to Middlesbrough, Preston and Newcastle. West Cumberland and Cumberland Infirmary are also taking in those injured.
Wounds range from cuts to spinal injuries.
Barry Pickthall, who runs coach firm JB Pickthall, said the coach involved was from his company and was carrying schoolchildren from Keswick High School.
Mr Pickthall said the 49-seater coach was not full but had about 30 pupils on board.
It had been on the school run, taking pupils to their homes in Cockermouth after attending school in Keswick, about 13 miles away.
Mr Pickthall said he was waiting to speak to police and had no information about what caused the crash.
Brian Lewis, who lives near the crash scene, said the school bus swerved to avoid a car before the collision.
He said: "It's a right mess, there are ambulances everywhere, it's a chaotic scene.
"The bus was taking the children home from school.
"The site of the actual crash is in a hollow so you can't see a huge amount from the fields nearby.
"It seems the bus was swerving to miss a car and another vehicle has crashed into it.
"Both have toppled over."
Tricia Kerr and her husband live near the crash scene. He heard a "terrible bang".
She said: "He could see there was a school bus and it was on its side and there was three cars."
In a statement, Cumbria County Council said a team of educational psychologists would be available at Keswick School from Tuesday morning to help people begin to come to terms with what had happened.