At least 11 people have been killed after dozens of cars and lorries were involved in two pile-ups on the Trakia motorway in south-eastern Bulgaria.
Health Minister Katya Ivkova said 10 people died at the scene, near the town of Zimnitsa, and one more in hospital. A further 46 people were injured, BTA state news agency reported.
Sliven region governor Mihail Kasherov told journalists at the scene that more than 70 vehicles were involved.
Officials have said dense fog reduced visibility and was the likely cause of the first crash, which occurred on the eastbound carriageway.
The second crash, on the Sofia-bound carriageway, was likely also caused by the fog, with drivers also distracted by the first crash, BTA reported an official as saying.
The Trakia motorway runs from west-to-east of Bulgaria, and cuts through the capital Sofia.
Road administration director Galin Kostov added that speeds were unsuitable for the conditions, which included wet road surfaces, and the motorway would remain closed until it had been cleared, BTA reported.
Yambol regional governor Georgi Chalakov said reports first came in at 07:10 local time (05:10 GMT), with the injured taken by ambulance to hospitals in the Yambol, Sliven and Burgas regions.
Chalakov told BTA rescue teams had to remove sections of the crash barrier to reach people. He added that the fog meant that helicopters could not be used in the evacuation efforts.
One witness who helped rescue a from a burning vehicle blamed "very thick fog" for the pile-up.
"I got out of the car, I ran forward and pulled that man out," the witness told Reuters news agency.
Another told Reuters that "many, many people died".
"As for me, there were four cars behind me - trucks - and I don't know how I got out or what happened, but in the end, thank God I'm still alive," that witness said.
Bulgaria Prime Minister Rumen Radev - who had been hosting European Commission President Ursula von der Leyen - cut short a news conference following the news.
