An investigation has been launched into the incident

The teenager was being transported to custody by Avon and Somerset Police when she got out of the vehicle between junctions 24 for Bridgwater and 25 for Taunton, Somerset, at about 23:00 GMT on Monday.

She died at the scene, and no-one else was injured in the incident.

The Independent Office for Police Conduct (IOPC) said an investigation had been launched, with a spokesperson saying: "Our sympathies are with the girl’s loved ones and everyone affected by her death."

They added: "We were advised by Avon and Somerset Police that the girl was being transported to custody in a police vehicle and had got out of the vehicle shortly before the collision.

"We sent our investigators to the police post incident procedure to begin gathering evidence."

Avon and Somerset Police said it had made a mandatory referral to the IOPC due to the recent prior police contact.

Following the collision, the M5 was closed in both directions, the BBC reports.

National Highways confirmed on Tuesday morning that the northbound carriageway had reopened between junctions 24 and 25. The southbound carriageway reopened shortly afterwards.

Anyone who witnessed the collision or may have dashcam footage which could help the investigation is urged to contact police by calling 101 and giving the call handler the reference of log number 1170 of 11 November.