Police are following up various lines of enquiry in relation 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 in Birmingham.
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 on Saturday.
Superintendent Sean Phillips, from West Midlands Police, told a press conference : "It is way too early to speculate on the causes of the accident.
"It will take some time to unpick the scene and just understand exactly what's happened. It would be unfair for me to speculate at this time."
He confirmed the road had been gritted at 5pm the previous evening.
Asked about what speeds the vehicles were travelling and whether all of those involved were wearing seatbelts, Supt Phillips said those will be issues considered during the investigation.
The Ambulance Service, which sent five ambulances and three paramedics to the scene, said it was astonishing that a man and woman in the first car were able to escape with minor injuries despite "extensive damage" to their vehicle.
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.
Police are working to contact families of those involved.
Images of the devastation in the aftermath of the crash have been shared online.
Supt Phillips urged people to send those images to police rather than posting them on the internet.
He said: "It's a harrowing scene. There are families involved, these are real people involved . It is very distressing for everyone.
"To share images that would portray something that is perhaps unwelcome for the families and unhelpful for the investigation at this time - I would urge people not to do that.
"I would urge them to contact police and share it with West Midlands Police. It will be treated as evidence and information that might help us piece together exactly what's happened."
West Midlands Fire Service said 40 firefighters helped in the aftermath of the "horrific" crash, and were met with what they described as a " complex scene, spread over some distance".
The road is likely to remain closed throughout Sunday, police said.