A man threatened a pensioner with a knife at a steam railway booking office before stealing more than £1,000.
The man, thought to be in his 40s or 50s, fled from the Launceston Steam Railway, in Cornwall, with a "four-figure sum" at around 16:10 BST on Sunday.
The elderly female shop assistant was described as "shocked, but unhurt".
A police officer, who tried to apprehend a man nearby, was assaulted and taken to hospital as a precaution.
The armed robber, who had his face covered with a scarf, entered the shop and threatened the assistant with a "sizeable knife".
The founder of the Launceston Steam Railway, which takes passengers on a five-mile round trip along the old North Cornwall line, said he believed the man made off with more than £1,000....
