Police spokeswoman Towe Hägg told The Local that police received a call about the attempted robbery at 3.30pm on Thursday. The attempted robbery took place outside the headquarters of Handelsbanken in central Stockholm.
Witnesses reported seeing masked men flee the scene and police said they received reports of smoke in Söderledstunneln, a major tunnel linking central Stockholm to the southern suburbs.
At the moment, police don't think there is any major threat to the public.
"We don't even know yet if they are armed," Hägg said.
As part of their search for the robbers, police ordered public transit operator SL not to trains to stop and let off passengers at several metro stations, including Kungsträdgården, T-Centralen, and Slussen.
The stations were not, however, evacuated of passengers.
Police officers were searching through the trash cans on the platform, The Local's reporter on the scene said.
The metro system returned to normal traffic at 4.10pm.
According to the latest police statement, the masked robbers fled the scene in two cars, but did not manage to get any cash in the robbery attempt.
In addition to reportedly dispersing smoke bombs in the tunnel, the four perpetrators also put caltrops out on the street near the Slussen metro station in what appears to be an attempt to slow down the police's pursuit.
Oliver Gee/Ann Törnkvist/The Local