A dozen elementary school students in New York City were hospitalized briefly on Tuesday after a smoke bomb was set off on a school bus, police said.
The bus was carrying about 40 children between ages 7 and 11 to a school in the borough of Brooklyn when the device went off, presumably set off by one of the students, said a spokesman with the New York Police Department.
Twelve students were taken to a hospital as a precautionary measure and were examined and released, police said.
Police said they were investigating who set off the device, a firework designed to emit plumes of thick smoke.
When detonated in a contained space, such a bomb can cause breathing problems and other medical conditions, police said.