Six people died and 27 others were injured in a series of multi-car collisions on Serbia's main highway on Tuesday morning, police said in a press release.
The accident took place around 7:20 a.m. (0520 GMT) near the city of Jagodina, some 100 km southeast of the country's capital Belgrade, according to the police.
The fatal collisions piled up in both directions of the highway, causing a complete collapse of traffic. Members of the police, together with rescuers, rushed to the scene.
Rescuers have been trying to free people, both locals and foreigners who were trapped in their vehicles, according to Serbia's public broadcaster RTS.
The injured, including three citizens from Greece, Poland and Germany, were transported to hospitals in the cities of Jagodina and Cuprija.
"The investigation is ongoing, while the traffic accident was most probably caused by the dense fog," police said.
RTS confirmed that at the time of collisions, the visibility in this part of the highway was decreased to just bellow ten meters as the dense fog rose from the Morava river nearby.
"There was some mist on the way, but when I passed Morava it had turned into a thick wall," said one truck driver who witnessed the event. "I immediately started to brake and stopped before the truck in front of me. I got out of my truck and saw that vehicles around me had already started to collide."
One truck caught fire and fire brigades and ambulances were at the scene, according to witnesses.