Two of the trains' tanks, carrying propane-butane and propylene, derailed at the station of the village, hit electricity line and exploded in flames early on Saturday, a senior police officer said.
"Two blasts have caused a serious fire and ruined at least 20 buildings. There are many people injured... many with burns," Interior Ministry Chief Secretary Georgi Kostov said.
Some 150 firemen are trying to put out the fire and are searching for survivors in houses near the train lines.
Police said they are investigating the incident.
Bulgarian Prime Minister Boiko Borisov is travelling to the village, some 280 km northeast of Sofia and home to around 800 people. Borisov appealed to Bulgarians in the northern city of Shumen to donate blood to the local hospital where the injured are being transported.
