Police have stormed a unit and arrested a man after an hour of negotiations following a stabbing in western Sydney.

Neighbours called police to a unit block on Graham Street in Berala about 9.55am today after hearing screams and finding a 45-year-old man with stab wounds on the driveway.

“My neighbour heard the screaming. When he came out and saw he was on the floor, he called me and called the police, and I called the ambulance,” a witness told 9News.

Another witness said the man had six stab wounds to his head and body.

Police said the man was seriously injured and taken to hospital in a stable condition.

Officers tried to speak with an armed man at the scene, but he barricaded himself inside a unit.

A perimeter was established and the community were urged to avoid the area as police negotiators, riot police and the dog unit were called in to help.

After an hour-long siege, police stormed the home about 11.10am and arrested a 25-year-old man.

He was treated at the scene for minor injuries before being taken to hospital for further treatment under police guard.

Police told 9News the pair are known to each other, but it is unclear what sparked the attack. 

Both men remain in hospital as investigations are ongoing.