Four firemen have been injured as a second explosion near Bulgaria's Black Sea city of Varna occurred in the train composition of propan butan-filled gas cisterns on Wednesday.

That was the second blast of a gas-filled auto cistern in the Bulgarian village of Ezerovo, in the district of the coastal city of Varna, for that day and it went off around 6.30 p.m.

On the scene there were dozens of firemen still putting out the fire caused by the same cistern which had exploded earlier the same day.

Around 4 p.m. on Wednesday the police reported an explosion of a gas cistern injuring two men. One of the men was accommodated at the Navy Hospital in Varna being in critical condition while the other man suffered no life-threatening injuries.

In a statement released by the police officers an hour and a half later, the fire triggered by the first explosion had been put under control.

One hour later, the second explosion took place, injuring 3 more.