Emergency services were called to the Esso Garage at Stockton Road in Seaham at around 4am on Sunday following an incident at the premises.
The site was reportedly cordoned off and two men have been arrested in connection with an attempted robbery at the petrol station.
Durham Constabulary confirmed that a 31-year-old man has been arrested on suspicion of robbery and being in possession of a “noxious substance”.
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Another man, aged 23, has also been arrested on suspicion of robbery.
A member of staff at the petrol station received treatment from the North East Ambulance Service at the scene for facial injuries
Officers have asked anyone with information about the incident to come forward.
A spokesperson for Durham Constabulary said: “Two men have been arrested in connection with a robbery at a petrol station in Seaham in the early hours of this morning.
“Police were called shortly after 4.15am to the incident at the premises in Stockton Road.
“A 31-year-old man has been arrested on suspicion of robbery and being in possession of a noxious substance and a 23-year-old has been arrested on suspicion of robbery.
“A member of staff was treated at the scene by paramedics for facial injuries.
“Anyone with any information is asked to call Durham Constabulary on 101, quoting incident number 65 of January 23.”
A statement from the North East Ambulance Service said: “We were called at 4:42am to New Seaham Service Station on Stockton Road. We treated a patient with facial injuries and they were discharged at the scene.”