The most likely cause of the Wednesday fire on the Sofia – Varna train is overheating, according to Bulgaria's Deputy Transport Minister, Kamen Kichev.

In a Thursday interview for the Bulgarian National Radio, BNR, Kichev pointed out Wednesday had been the hottest day of 2011 so far and overheating had sparked the locomotive fire.

"The terrain was very difficult; we had a hard time reaching the scene. For this reason and because of the scorching heat and the wind two train cars also burned out by the time the fire trucks arrived. When you have temperatures of 40 degrees Celsius even a brand new locomotive can catch fire," the Deputy Transport Minister explained.

Miraculously, there have been no injuries in the latest train incident in Bulgaria, which happened after Train No. 2615 of the Bulgarian State Railways BDZ caught on fire on the route from the capital Sofia to the Black Sea city of Varna.

The fire in the Sofia-Varna train erupted shortly before 6 pm on Wednesday in its locomotive near the village of Resen, Veliko Tarnovo District.

The train was stopped and the 214 passengers were evacuated intact. However, the fire spread to the first two passenger cars before the fire brigade units arrived at the scene, more than an hour after the fire started, because of the rough terrain.

The incident with the Sofia-Varna train is the latest in a string of increasingly serious incidents.

On June 29, 2011, a local train between Cherven Bryag and Montana in Northwestern Bulgaria had to stop near Vratsa because of a fire on board, without any victims.

On June 10, 2011, the locomotive of a freight train also caught on fire near Simeonovgrad in Southern Bulgaria, with the driver managing to flee intact.

The most severe train incident in Bulgaria since 1992 was also caused by a train fire when 9 persons were burned to death, and 9 others were injured in the night Sofia-Kardam train in February 2008 near Cherven Bryag.