Police have appealed for witnesses to a multiple vehicle crash in which six people died, as they work to understand what caused the "harrowing" collision.

Three men were killed when they were thrown out of their car while a black cab driver and his two passengers, a man and woman, died after the vehicle was left on its side.

A fourth man travelling in the car remains in a critical condition at the city's Queen Elizabeth Hospital.

Police said they are following various lines of investigation including the condition of the road when the crash happened at Belgrave and Lee Bank Middleway, near Edgbaston, at the junction of Bristol Road shortly after 1am.

Three other cars collided as they tried to avoid the scene at the entrance to the underpass.

Of those people, two were taken to Heartlands Hospital with minor injuries.

The ambulance service said they dealt with 13 patients in total.