Detectives are questioning two men after four people died when a quad bike collided with a sports car.
A woman aged 18, a girl of 16 and a 20-year-old man on the quad bike were confirmed to have died at the scene between Upton and Hemsworth, West Yorkshire, while a second 20-year-old man later died in hospital of his injuries.
The two men and the 18-year-old woman have been named in reports as Ryan Beal, Brandon Brown and Alexandra Binns.
Officers were called at about 12.34am on Sunday to a report of a collision between a bronze Nissan 350Z sports car and the quad bike on the A6201.
Two men aged 21 and 22, who were in the car, were arrested on suspicion of dangerous driving and remain in police custody.
Detective Chief Inspector Richard Holmes from the homicide and major inquiry team, who is leading the inquiry, said: "Widespread investigations are continuing into what is a significant incident on the district's roads which has now tragically resulted in the loss of four lives.
"Painstaking investigative work is continuing. The victims are from the local area and are two men aged 20 and two females aged 18 and 16.
"Their families are currently being supported by specially trained officers and we are not in a position to release any further details of those who have lost their lives at this time."
He added: "We continue to appeal for witnesses to the collision and would also like to speak to anyone who may have seen a unregistered quad bike driven on the roads around the Hemsworth area in the evening of September 26 and up to 12.30am on September 27.
"Similarly I would appeal for any witnesses who saw a bronze-coloured Nissan 350Z driven in the Hemsworth area on the evening of September 26and up to 12.30am on the September 27 to come forwards.
"Anyone who has information is asked to contact the major collision and inquiry team on 101."