It happened at about 4.55pm yesterday on the A653 Dewsbury Road in Morley, near to the entrance to Topcliffe Grange Farm.
The crash involved a white Skoda Octavia taxi, a black Suzuki Swift, a white Vauxhall Vivaro van, and a black Audi A3.
At the time of the crash, the Skoda had been travelling from the farm entrance road to turn right onto the southbound dual carriageway and the Suzuki was heading north towards Leeds.
The Suzuki lost control and crossed the central reservation into the southbound carriageway where it crashed with the Vauxhall and the Audi that were both travelling south towards the M62.
The driver and front seat passenger of the Suzuki, both 19-year-old men, and a 42-year-old woman, who was the front seat passenger in the Audi, all received serious injuries.
They are all in a critical condition in Leeds General Infirmary.
The driver of the Audi, a 43-year-old man, and a nine-year-old girl who was in the car were taken to hospital with injuries that were not considered life threatening.
The Vauxhall driver, a 49-year-old man, and front seat passenger, a 46-year-old woman, both received slight injuries.
The driver of Skoda, a 37-year-old man, was not injured and has been interviewed by officers.
Anyone who witnessed the collision or the circumstances leading up to it, particularly anyone with relevant dashcam footage, is asked to contact the Roads Policing Unit via 101 quoting log number 1165 of December 22 or online via www.westyorkshire.police.uk/101livechat