Burnt out and crushed vehicles were strew across the motorway in the aftermath of the crash

Twelve people have been killed after dozens of cars and lorries were involved in two pile-ups on the Trakia motorway in south-eastern Bulgaria, Prime Minister Rumen Radev has said.

Health Minister Katya Ivkova said 11 people died at the scene on Tuesday, near the town of Zimnitsa, while another person later died in hospital. About 50 others were taken to hospital with injuries.

Sliven regional governor Mihail Kasherov told journalists that more than 70 vehicles were involved in the incident, Bulgarian state news agency BTA reported.

Officials have said dense fog reduced visibility and was the likely cause of the first crash, which occurred on the eastbound carriageway.

Radev declared Wednesday a day of national mourning following the incident.

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 connects the capital Sofia to the Black Sea coast.

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.

A drone captured the scene from above, just visible through the dense fog

One witness who helped rescue a man 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.

Radev - who had been hosting European Commission President Ursula von der Leyen - cut short a news conference after learning of the incident and visited the scene.