Pupils of Chapel Street Primary School in Woodstock will be in for a shock when they return to school next week: a section of the historic building has been gutted by fire.

Jamiel Alexander, principal of the 97-year-old school, said neighbours had seen two boys on the premises just before the building went up in flames.

The fire started at about 5.30pm on Wednesday and neighbours called the fire department when they noticed thick black smoke.

By 7pm, the fire had been doused and all that remained of the building were smouldering charcoal beams, ash and sheets of corrugated iron.

Alexander said he was grateful that it was only the storage shed that was affected, as the rest of the school was in a separate section.

The storeroom housed a few desks, fabrics and other flammable objects.

The school, which still has quaint separate entrances for boys and girls, has been declared a national monument, according to Alexander.

He has been principal there since 1994, but prior to that had been a teacher at the school for more than 30 years.

In that time, he said, they had been fortunate to have avoided any kind of serious incidents at the school.

"I will report this to the Education Department immediately, and hope they treat this as an emergency," said Alexander.