Five men who were all wearing balaclavas have broken into a lorry and stolen a quantity of cigarettes.
The gang, who were all dressed in black, pushed a woman who challenged them during the theft on Newport Road, Caldicot, at 0650 GMT on Thursday.
Gwent Police are appealing to anyone offered the cigarettes for sale to contact them immediately.
The robbers made off on foot in the direction of Jubilee car park where it is thought they had a vehicle waiting.
Police say the men were challenged by the driver of the lorry which was parked and a female member of the public.
Although she was pushed she was not injured.
Witnesses or anyone offered the cigarettes should contact Gwent Police on 01633 838111 or Crimestoppers on 0800 555111.