"The ammonia leak caused 51 cases of poisoning," Vasic said during a press conference.
According to the mayor, seven people were hospitalized.
A major highway was closed down on Christmas and several cars crashed in the city due to low visibility caused by the leak.
Earlier in the day, the Serbian Interior Ministry said the train derailed in the evening, causing a leak of ammonia and a large amount of gas released into the atmosphere, urging local residents not to leave their homes.