The CTA said that there was a "mechanical issue [and] minor smoke that quickly dissipated," but some riders were concerned given last week's shooting on a train in New York City. Some passengers were reportedly screaming in panic.
On Twitter, Ling Luo said: "It seriously reminded me of what happened in NY, but fortunately not. The blue line train was stopped at Logan Square when it happened."
Other passengers also shared videos of people hustling off the trains as smoke poured across the ceiling of the train station.