Bus explodes in centre of Stockholm, Sweden

A large explosion rocked the centre of Stockholm yesterday.

A natural gas-powered bus didn't have any passengers on-board when it caught fire from an explosion in Sweden's capital, near the government district.

Stockholm police said there were no signs it was terror-related.

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 passengers in the bus. I do not know how it is with the driver, but I have no information that someone is injured," Police press officer Carina Skagerlind said, according to Aftonbladet.

"I heard a big bang first and then several smaller ones. It seemed like a scaffolding collapsed," one witness told the publication.

Rescue worker Asa Skold told the Swedish newspaper 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.

Stockholm fire and rescue officials were called to the Klara Tunnel in central Stockholm at about 11:25 a.m. local time.

The department said the incident was being investigated as a traffic accident.

Shocked locals have shared video and photos on social media showing large plumes of black smoke rising high over the buildings.

Swedish Transport Administration says the explosion will have a "very great traffic impact" and flow on effect into the rest of the weekend with two tunnels - the Klarat tunnel and the Söderled tunnel - closed as a result of the incident.