Police and rescue services were alerted to the scene shortly after four o'clock.
The blast took place outside a restaurant near St. Mary's Church.
Exactly what it is that detonated is unclear at the moment.
The police have cordoned off a large area around the site, as there is a lot of broken glass on the ground.
Several adjacent properties have also had their windows smashed.
- It must still have been quite powerful, says Peter Martin, officer on duty.
Strong bang
He describes that the explosion took place in a fairly closed place where the pressure can bounce between properties.
Which can lead to even a smaller charge can do greater damage.
The rescue service confirms that it was a loud bang.
- The police may take over and investigate what happened, but it is a powerful explosion, says Lars Rundh, internal commander of the rescue service.
The police are investigating the whole thing as gross general destruction.