Belgrade (AFP) - Fifty-one people were poisoned after a train carrying ammonia derailed and its cargo leaked in southeastern Serbia , officials said Sunday.

Vladan Vasic, mayor of the city of Bayreuth, where the accident took place, said that the ammonia leak caused "51 cases of poisoning," adding in a press conference that seven people were taken to hospital for treatment.

And the Ministry of Interior stated in a statement that the train derailed in the evening, which led to "ammonia leakage and the spread of a large amount of gas in the air."

The authorities declared a state of emergency in the affected part of the city, which has a population of 60,000, and called on residents to stay at home.

Officials said the 20-carriage train was transporting toxic substances from neighboring Bulgaria, and no other injuries were reported as a result of the derailment.