- Blast damaged more than 50 buildings in village of about 800 people
- It's not yet known what caused the cargo train to derail
The blast damaged more than 50 houses and public buildings in the village of Hitrino, and dozens of homes have been evacuated, the ministry said.
At least 12 people were rescued from the damaged buildings, according to the ministry. Firefighters were trying to extinguish flames, cool the overturned gas tankers and search for any other survivors.
Prime Minister Boyko Borisov went to the village after the explosion. It wasn't immediately clear what caused the derailment.
Hitrino is a village of about 800 people about 300 kilometers (186 miles) northeast of Bulgaria's capital, Sofia.