A major police operation in Sydney's south-west that lasted more than five hours has concluded with no arrests and "nothing of interest found".

NSW Police officers locked down a Punchbowl street in a show of force on Wednesday afternoon after a man was detained and assaulted.

A spokeswoman for NSW Police said the man who was allegedly assaulted suffered minor injuries and is now with police.

Officers from Bankstown and Campsie area commands established a perimeter around 3pm and specialist police are on the scene, the spokeswoman said.