A mysterious explosion at a secondary school in the Swedish city of Karlstad is being investigated by emergency services.

There was no immediate indication that the incident was linked to terrorism or any form of attack, Swedish journalist Stefan Björklund told ITV News.

Police and fire crews were on the scene, but there were no injuries initially reported.

The "powerful" blast reportedly happened in the sports hall at the Tingvallagymnasiet at around 2.45pm.

There were some reports smoke was seen coming from the site.