A woman has died following a pile-up involving around 20 vehicles on a major road in England.
The A40 has been closed in both directions following the multi-vehicle crash, which stretched for more than half a mile (1km) on the A40 near Witney in Oxfordshire, the ambulance service said.
The woman driver was declared dead at the scene, while another person was taken to the major trauma unit at the nearby John Radcliffe Hospital in Oxford.
A further 10 to 15 casualties were treated at the scene following several collisions at around 8.25am, South Central Ambulance Service spokesman David Gallagher said.
Images showed the mangled wreckage of several of the cars involved, with debris strewn across the road.
Six vehicles were said to be badly damaged, while a further 10 to 15 were also involved, with the most serious injuries happening in the middle of the pile-up.
The incident is likely to cause major disruption for many people travelling across the country following the Christmas break, as the road connects London to Wales.
Mr Gallagher said: "There was a collision towards the front of the queue and the more serious one about half-way down."
He added three ambulances, three rapid response vehicles and two ambulance officers and an air ambulance car had attended the scene.
A Thames Valley Police spokesman said: "Thames Valley Police officers were called today at about 8.25am following reports of a collision involving multiple vehicles on the A40, Witney.
"Officers are at the scene along with the fire and rescue services. A number of people are believed to have been injured.
"Road closures are currently in place, and drivers are advised to avoid the area."
Pregnant mother-of-two Ami Gaston, from Carterton, was in the car with her partner when she saw the first vehicle crash. She said the accident happened about half a mile from the Witney exit, blocking the right lane.
"A man on his own had skidded and crashed into middle barrier. My partner was driving - we had to swerve out of the right lane to avoid hitting him. His door was open and air bags were released," Miss Gaston said.
"I phoned an ambulance but couldn't stop. My partner wouldn't stop because I am 20 weeks pregnant and didn't want to put us in danger."
She added that the heavy fog meant the situation was "really dangerous", as it was difficult to see any other car until you were "on top of it".
Another eyewitness arrived at the scene later and described the "carnage" as multiple cars swerved and crashed on the busy road.
The woman, who asked not to be named, said she "luckily" saw hazard warning lights ahead as she approached on the slip road from Carterton, and moved on to a grass verge before witnessing the pile-up.
"I saw cars going zooming past me and trying to swerve out the way of the stationary cars but crashing into them," she said.
"I saw one car try swerve in between a Mini and another car, ending up crashing into the Mini and (flying) up in the air.
"I saw two cars swerve as they braked so hard and go flying into the barrier in the middle of the road ... it was carnage," she added.