London - A class of British school children sitting exams had a lucky escape when a heating duct collapsed in a gym, injuring 13 pupils, four of them seriously, the emergency services said.

The 14-to 15-year-old pupils at Minster College in Sheerness, on the coast of Kent, southern Britain, had just started the exam session when the duct collapsed.

The fire services said the class had been "very very lucky," as the duct had fallen between rows of pupils.

The injured pupils were all taken to hospital, and the school was closed for the day.

Four of them suffered serious head, neck and back injuries, the ambulance service said.

Head teacher Alan Klee said the school's first aid-trained staff had given immediate assistance to the injured pupils and those suffering from shock. (dpa)