The women, aged 27 and 31, are believed to have been thrown from the blue Ford Focus ST following the accident in Birmingham.
They are both still in hospital, while the alleged driver has been released by police pending further investigation.
The 30-year-old suspect was checked over in hospital before being arrested on suspicion of dangerous driving and drink-driving. A third passenger, a man aged 28, was taken to hospital with minor injuries but released a short time later.
The crash happened on Alcester Road in Moseley, near the junction with Sandhurst Road and Woodnorton Drive, at around 12.40am on Saturday.
Sgt Dean Caswell, from West Midlands Police's Serious Collision Investigation Unit, said: "I need to hear from anyone who saw the collision, or who may have dash-cam footage of the Focus driving along Alcester Road out of the city from the direction of Moseley. I'd also like to speak to four Asian men who helped the injured at the scene."
Anyone with information has been asked to get in touch via Live Chat at west-midlands.police.uk, or via 101. Quote log 93 of 25 January.