A group of between three and five men carrying weapons raided Watchfinder at the Victoria Quarter in Leeds at about 6.46pm.
Police received various reports about the weapons the men were carrying, but some reports suggested that the men were carrying firearms. No shots were fired and no one is believed to have been injured in the incident.
A large quantity of jewellery was stolen.
The men made off from the scene in a high-powered blue Audi in the direction of East Gate.
West Yorkshire Police were called and attended the scene immediately.
A spokesman for the force said: "A large quantity of jewellery was stolen and an investigation is ongoing to identify the suspects.
"At this time we are still in the process of the investigation."
If you have any information, please call police on 101 or Crimestoppers on 0800 555 111