A natural gas-powered bus that didn't have any passengers on board caught fire from an explosion in Stockholm on Sunday.
The city's police department tweeted that the bus driver was rushed to the hospital with severe burns but no one else was known to have been injured.
There were no signs it was terror-related and it is being investigated as a traffic incident, police said.
Photos and video footage from the scene showed the bus in flames and thick black smoke.
Stockholm fire and rescue officials were called to the Klara Tunnel in central Stockholm at about 11.25am local time.
Rescue worker Asa Skold told Swedish newspaper Aftonbladet the bus appeared to have collided with barriers at the top of the shallow tunnel's entrance, causing a gas tank on the vehicle's roof to explode.
The newspaper said the out-of-service bus was on its way to a bus depot.
