A masked man escaped from police when they disturbed him performing a smash and grab raid on G & B Griffin jewellers, Three Horse Shoes Walk, Warminster, at 4.50am on Monday.
He got away with 30 watches when he smashed the window of the shop but was disturbed by British Transport Police Officers who were driving through the town at the time.
They gave chase but failed to catch him as he ran off in the direction of East Street.
Police describe him as white and about six foot tall.
He was wearing dark clothing and his face was covered with either red and white clothing or a bandana.
Anyone with any information on the incident should contact 101 or call Crimestoppers anonymously on 0800 555 111