A worker has been injured in a string of aggravated robberies carried out by youths in Christchurch this morning.

At 8.30AM offenders walked into a dairy on Somerfield Street and attacked a staff member. The robbery was captured on CCTV.

A police spokeswoman said officers were still investigating the aggravated robbery, where the offenders, using a tool as a weapon, struck the worker, causing minor injuries.

A St John spokeswoman said they responded with an ambulance, and assessed and treated one patient in a minor condition at the scene.

The offenders are believed to have used a stolen car.

A similar incident then occurred at the Challenge service station on Blighs Road, and again at a dairy on Clyde Road, although it is understood staff were not injured in those attacks.

A commercial helicopter has been brought in to help police track the offenders, who dumped their stolen car in Kaiapoi.