The attack happened in King Street, just outside Barclays, at 11.45am today.
Northumbria Police has said the guard, was threatened with a knife, but not injured in the robbery.
The attackers ran off with a cash box and searches are being carried out in the area.
The man is described as being 6ft tall and of slight build. He was wearing a blue bobble hat, and was believed to be with a second male.
A marked police van has been outside the bank in the wake of the incident, with the area cordoned off.
Inquiries are ongoing and officers remain in the area to carry out searches and to reassure members of the local community.
The guard worked for G4S.
Area Risk Consultant for G4S Cash Solutions, Duncan Watson said: "On Tuesday 13 February, one of our cash crews was the victim of a vicious attack during a routine service on King Street in South Shields. Fortunately our colleague has not suffered any serious injuries but understandably has been left very shaken by the attack.
"We are working closely with Northumbria Police and I would urge anyone who may have been nearby and seen this attack to get in touch with the police or dial 101 so that those behind it can be brought to justice."
Anyone with information is asked to call 101 or Crimestoppers anonymously on 0800 555 111.
