'Powerful explosion' at school in Sweden

A 'powerful explosion' has been heard at a school in Sweden.

The blast was reportedly at a secondary school in the centre of Karlstad. Local authorities said it came from within the school, possibly from the gym.

"We are on site now and are trying to ascertain what has exploded," Ola Akesson of Karlstad’s emergency services told Swedish newspaper Expressen.

Police said they searched the building for more than an hour but could find no trace of the cause of the explosion.

A statement post to Facebook said: "We now have over an hour investigated what may have been the cause of the blast in central Karlstad.

"We find no explanation. Our theory is that someone has gone off of something that has not left any trace behind.

"No one has been injured in the explosion and teaching at Tingvallagymnasiet continues as usual.