Security guards at Santander have been robbed by armed raiders in a second heist at the same bank in two months.

Two masked thieves followed two G4S guards in the early hours of Wednesday as they carried a cash box into the bank in Helensburgh, Argyll.

The raiders, who were dressed in overalls and masks, then threatened the pair with weapons and made off with the cash at Santander on West Princes Street at around 12.35am. It is believed they made off in a dark 4x4.

Police are appealing for information on two cars seen in the area around the time of the robbery.

One is a white Audi TT seen on Sinclair Street, West Princes Street and last seen heading towards James Street.

The second car is described as a dark-coloured people carrier, possibly a Vauxhall Zafira, seen on East Princes Street.

Detectives are appealing for the occupants of both vehicles to get in touch as quickly as possible.

An almost identical raid happened at the same bank at around the same time on Wednesday, April 6, in which G4S employees were again targeted and robbed of more than £10,000.

Police believe both heists are linked and have launched a major investigation to trace the raiders.

The suspects are described as being of medium height, medium build and were wearing overalls and masks at the time of the incident. The employees were not injured but were left shaken as a result of the incident.

Detective inspector Douglas Wilson, of Argyll and West Dunbartonshire CID, said: "This incident follows a similar incident which took place in the early hours of Wednesday, April 6. One line of inquiry at this time is that these incidents are linked.

"Two men entered the premises of the bank, by means of the window, threatened the men with weapons and then made off with the cash box in an unknown direction - possibly using a dark coloured 4x4 vehicle in their escape.

"Officers remain at the scene on West Princes Street and local door-to-door inquiries are under way.

"Specialist officers are analysing available CCTV. A dedicated incident room has been established at Helensburgh Police office.

"Our inquiries are at an early stage. At this time, we are asking that anyone who may have witnessed the incident, or heard a disturbance in the area in the early hours of this morning, to please contact officers as soon as possible."

Anyone with information is asked to contact officers at Helensburgh police office via 101. Alternatively, please call Crimestoppers on 0800 555111, where information can be given anonymously.