A man is believed to have been been shot at a railway station in Sydney’s south.

NSW Ambulance officials say the man, in his 30s, was shot at Campbelltown station on Wednesday afternoon before being rushed to Liverpool Hospital.

Police have confirmed an operation is under way in the area.

Police say the man challenged officers with a knife before he was tasered and then shot.

“Police deployed a taser, however he continued to threaten police, before being shot,” a spokesperson said in a statement.

“The man was taken to Liverpool Hospital suffering a single gunshot wound to his stomach.”

There were reports he was being chased by officers on foot about 2.30pm when he turned around, pulled out a knife and lunged towards them.

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A crime scene has been established on Hurley Street and a critical incident investigation launched.

No officer or other members of the public were injured, detectives say.

Police have flooded the station and cordoned off the area as part of their developing operation.

Callers to Sydney radio 2GB said the operation was was causing traffic chaos.

“There’s traffic absolutely everywhere,” the caller said.

“It’s a nightmare at the moment, coppers absolutely everywhere.”

Authorities have warned of widespread delays in the area, particularly for commuters trying to travel through Campbelltown station.

–more to come

-with AAP