The drama began at around 6:15am when two security guards were delivering cash to the store to replenish the cash machines on the site at Amounderness Way.
As they left their vehicle with the cash box to make the delivery, they were approached by a male wearing a black balaclava who demanded they release the cash box.
In an attempt to ensure his own and his colleagues safety, the guard carrying the box dropped it and the offender took it and made off with the box which contained a significant amount of money.
The offender has been described as approximately 5 feet 9 inches tall and of medium build and wearing a dark grey tracksuit top.
Detectives are appealing for witnesses who may have been in the area or travelling along the main arterial routes such as Amounderness Way, the A583 and the A585 between 6am and 6:30am to come forward and contact DS Dave Reeder at Fleetwood CID on (01523) 604343.
A police spokeswoman said: "Our investigations are continuing but information could be crucial."