Security guards patrolling the station in the northern suburb of Stockholm raised the alarm at around 7pm. The object is thought to have been thrown into the station from Tensta square.
“It was some form of smoke or gas which caused irritation of the eyes and made it hard to breathe,” said Björn Engström, spokesman at Stockholm police.
Ambulances were called to the scene to treat those affected by the smoke. Late on Wednesday evening police said they did not yet have any idea who had let off the bomb but that the crime was being treated either as endangering others or as assault.
At 7.50 pm train traffic between Rinkeby and Hjulsta was stopped for the rest of the evening.
According to SOS Alarm, none of those affected by the gas needed to be taken to hospital.
“Those who had difficulties were treated at the scene,” said Björn Engström to TT.