The accident caused long queues across the capital from around 6am onwards, with authorities predicting delays until late in the morning.
The incident occurred on Mäster Samuelsgatan, in central Stockholm, when a large crane got wedged at the entrance of the Klara tunnel.
"There's no risk of the tunnel collapsing," Albin Näverberg of the Stockholm police told the Aftonbladet newspaper.
A tow truck is currently on the scene, trying to drag the crane out of the tunnel.
More to follow