A police operation was underway at a police station in a suburb in the west of Sydney, Australia's largest city, emergency services said on Tuesday, with domestic media reporting at least one person had been shot.
A police spokeswoman said an operation was underway at the station in Quakers Hill, a suburb 40 km (25 miles) west of the city's central business district. No further details were available immediately.
Australia is on heightened alert for attacks by home-grown militants. Authorities say they have thwarted a number of potential attacks, although there have been several "lone wolf" assaults in recent months.
An accountant working for the New South Wales state police was killed when a 15-year-old boy opened fire outside police headquarters in the suburb of Parramatta, also in Sydney's west, in October last year.
The teenager, Farhad Khalil Mohammad Jabar, was killed in a subsequent gunfight with police.