It is understood the robber threatened the worker with a gun before making off with an unknown amount of money.
As reported in late editions of yesterday's Evening Times, a police probe is under way after the incident outside a shop in Uddingston, South Lanarkshire.
Officers were called to the scene in Old Edinburgh Road after 9am yesterday.
It is understood no-one was injured, although the security worker was left "shaken".
The exact amount stolen in the raid is not yet known.
Police said the investigation was at an "early stage".