Police in Australia have shot a man after he allegedly threatened staff at a Sydney hospital with a knife.

The suspect is said to have sustained a gunshot wound to the stomach after approaching officers with the weapon.

He is undergoing emergency surgery in the same hospital and is under police guard.

Emergency services temporarily stopped staff and patients from entering or leaving Nepean Hospital in the west of the city after the incident.

Surrounding roads were closed and there was a large police presence at the scene

No staff were injured, Australian broadcaster Nine News reported.

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Police were called to the hospital in the western suburb of Penrith shortly after 4pm local time on Wednesday.

Australia's Daily Telegraph newspaper reported that the suspect was a patient who brandished the knife in the entrance to the hospital before police intervened.

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Unconfirmed reports also said the man was carrying a note claiming to have an explosive device in a vehicle parked in the hospital's car park.

Brett Williams, general manager at Nepean Hospital, said the emergency department had been "temporarily closed following a shooting".

He added that staff were able to leave the building using a designated exit but that there would be a delay in accessing the hospital's car park.

Nepean Hospital is a private clinic that treats patients from Sydney and the nearby Blue Mountains.