Sofia - All seven passengers in two cars were killed Sunday when their two cars collided head-on in central Bulgaria Sunday morning, police said.

One of the two vehicles exploded in flames following the collision near Plovdiv, Bulgaria's second-largest city, 120 kilometres east of the capital Sofia.

Witnesses said the victims in the burning vehicle survived the initial crash, but perished in the fire. Three of the victims were teenage girls, while the others were men aged 23-44.

Police said they were still investigating the cause of the crash. The car that exploded was apparently equipped with a liquid petrol gas reservoir.

Reflecting on the deadly combination of reckless driving and the poor condition of Bulgarian roads, local media often refer to traffic casualties as victims of the "war on wheels."

Official figures say 248 people were killed on the roads of the new EU member state in 2008. (dpa)