Dangerous thugs, believed to be armed with a sawn-off shotgun, were on the run in York today after robbing a security van at a city petrol station.

Police combing streets around Chapelfields warned the public to be on their guard after a security guard was sprayed in the face with a noxious substance, possibly ammonia.

The guard was being treated at hospital for his injuries after the attack at the BP Inner Space petrol station in York's Boroughbridge Road, just before 10am.

He was not thought to be seriously hurt, and a woman guard also in the van escaped unhurt.

The three robbers, dressed in what are described as 'boilersuits', escaped on foot with a 'substantial amount of cash', climbing over a fence and heading off in the direction of the Chapelfields area.

The area was sealed off today as police including dog handlers and members of North Yorkshire police's armed response unit were called to the scene.

Detectives were also conducting house to house inquiries.

Members of the public were warned to avoid the men at all costs.

Det Insp Geoff Dodd of York CID said: "The police regard these men as dangerous. Police are treating a report that a sawn-off shotgun was seen as serious."

It is understood the Securicor van had arrived at the petrol station to service an automatic bank teller machine with cash.

Witnesses described seeing "at least" three men, dressed in boilersuits, loitering around near the scene of the raid before 10am.

Det Insp Dodd said the security guard who was sprayed in the face needed medical attention, but was not thought to be seriously hurt.

Speaking from the scene of the crime today, Insp Howard Harding said the raiders did not enter the garage shop and its staff were not injured.

Police today appealed for anyone who witnessed the robbery, or might have information about it, to contact them in confidence on York 631321.

Appealing for help from the public, he said descriptions of the robbers so far were still vague.

He said: "We have not had a lot of witnesses come forward at this point and we request that the public assist us."

A Securicor spokesman said a reward of up to £5,000 would be offered for information leading to the arrest and conviction of the raiders.

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