At least five people died and 27 were injured Saturday when a freight train derailed following an on board explosion in the Bulgarian village of Hitrino, police said.

Authorities fear the death toll could increase as some of the injured suffered 99 percent burns to their bodies, acting Prime Minister Boiko Borisov told Bulgaria's Nova television at the site of the accident, some 360 kilometers (224 miles) from the capital of Sofia.

There would be more than five deaths and the material damage caused was enormous, the Bugarian leader said, adding that according to an engineer one of the tank cars had detatched from the convoy before derailing.

Borisov called on citizens to donate blood at hospitals in the area, an appeal reiterated by President Rosen Plevneliev.

Four of the injured were taken to Varna's military hospital, 100 km from the scene.

The accident happened at around 5.45 am local time when the convoy made up of 26 tank cars, three holding propane-butane and 20 carrying propylene, derailed as it passed through Hitrino.

The country's fire department chief Nikolay Nikolov said one of the tank cars carrying propane-butane produced the explosion that led to the destruction of nearby buildings and caused a large fire.

Some 12 people have been rescued from the debris, he said, adding the town, which has a population of about 900 people, was being evacuated.

At least 20 buildings were destroyed in the incident, including the train station and a police station.