A teenage driver and her female passenger have died and three men are in hospital after their car careered off the road into undergrowth.
The grey Renault Clio carrying the three men and two women was found badly damaged 20 metres from the road.
All five people in the car, aged 19 and 20, are from the Swindon area, Wiltshire Police said.
The accident happened at 5am on the northbound A419 just past its junction with the A420 in Swindon.
Police were alerted by a driver who reported seeing the car leave the road.
"The 19-year-old female driver was pronounced dead at the scene. A second female was later pronounced dead at Great Western Hospital (GWH)in Swindon," a police spokesman said.
"Two of the male passengers are described as being 'very poorly' at Frenchay Hospital in Bristol. A third male is being treated for his injuries at GWH."
He added: "The northbound carriageway of the A419 will be closed for the time being from the junction with the A420 to the Turnpike junction at while a thorough police investigation is conducted. The southbound carriageway remains open."
Wiltshire Police are appealing for witnesses to call 101 and ask for Pc Kevin Fry of the serious collision investigation team.