STAFF and customers were evacuated from Barclays Bank in Victoria Square after the building's security system was activated and the building was filled with smoke.

Police and staff said the "smoke cloak" – intended to be deployed in the event of a robbery – was activated at 12.50pm.

Because the bank goes into "lockdown" when the alarm is triggered, some staff in the back of the building were unable to leave until the smoke had dissipated from the lobby.

It is not known exactly how or why the security system was triggered, but police said it had been activated accidentally by staff.

Some staff stood outside in Victoria Square while the glass-fronted building was visibly full of smoke.

Personal banker Mike Devine, aged 42, said: “I was just coming downstairs and the place was filling with smoke.

"No one seems to know why it was activated. This has never happened before during my time here.”

The bank was reopened at 3pm and no staff or customers are thought to have been hurt.

Bank staff refused to give any more details about what had happened.