A fourth person has died after a quad bike collided with a car.
Police said the vehicle collided with a bronze Nissan 350z sports car on the A6201 between Upton and Hemsworth at around 12.30am on Sunday.
Two girls, aged just 16 and 18, and a 20-year-old man were confirmed dead at the scene.
A second 20-year-old man was taken to hospital with critical injuries to his head and body.
He died at Leeds General Infirmary on Sunday morning.
Two men, aged 21 and 22, in the Nissan were arrested on suspicion of dangerous driving and remain in police custody.
DCI Richard Holmes, from the Homicide and Major Enquiry Team, said: “Widespread investigations are continuing into what is a significant incident on the district’s roads which has now tragically now resulted in the loss of four lives.
“Painstaking investigative work is continuing at the scene and the road itself will not be re-opened until tomorrow.
“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.”
“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 Saturday, September 26 and up to 12.30am on Sunday, September 27.
“I would appeal for any witnesses who saw a bronze coloured Nissan 350Z driven in the Hemsworth area to come forward.”
Anyone with information should call the Major Collision and Enquiry Team on 101.