Masked raiders made off with £650,000 of antique jewellery after breaking into a Gloucestershire school.
Police say a gang of up to six people broke into Westonbirt School at 0240 BST on Sunday.
The school, near Tetbury, was hosting the annual South Cotswolds Antiques Fair at the weekend.
The intruders set off alarms and were confronted by security guards, but threw furniture and sprayed a fire extinguisher at them before escaping.
They made off in three cars, one of which is believed to have been a silver estate.
The vehicles were last seen driving off the A419 near Cirencester Town football club.
Detectives say some of the stolen jewellery dated back to the Victorian and Edwardian periods.
One of the security guards was slightly injured in the attack, but did not require hospital treatment.