AN ARSON investigation is under way after a boy was trapped in a Gwent school when fire broke out.

The boy, believed to be 11 or 12, phoned 999 on his mobile phone and was rescued from Caldicot Comprehensive School by firefighters.

The blaze started outside the lower-floor boys' toilets in the Greyhill building yesterday morning. Gwent Police say they are treating it as arson.

According to a South Wales Fire Service spokeswoman, the pupil phoned at 8.42am and the school put in another emergency call a minute later.

She said: "When he rang our control, he was given fire survival guidance to ensure he didn't panic.

"He would have been told to get close to the ground to avoid as much smoke as possible."

Fire surrounded the exit of the toilet and two firefighters wearing breathing apparatus had to put it out before carrying the boy to safety.

According to the spokeswoman, there was a "considerable" amount of smoke.

The boy was treated by paramedics and then taken to Newport's Royal Gwent Hospital. He was later described as "fine" by a spokeswoman for Monmouthshire county council, and was being taken home.

A spokeswoman for Gwent Police said: "Investigations are ongoing into the fire, which we are treating as deliberate."