Emergency services were called to a home in the northern NSW city of Tamworth about 4.30pm on Saturday.
On arrival, police found a 47-year-old man suffering critical head injuries and a 55-year-old male armed with a knife.
The armed man locked himself in a bedroom before climbing onto the roof of the two-storey residence.
Wearing what appears to be a long jacket or robe over a t-shirt and shorts, he began screaming obscenities at police, some heavily armed and in riot uniforms, as they tried to gain access.
Footage on social media sites of the incident shows the man behaving erratically, running from side to side, as officers try to place a ladder against an eave so they can reach him.
On one point he lunges at the ladder, pushing it off its footing.
An officer armed with a protective shield who finally manages to climb onto the roof then chases the man before he leaps and lands on a first-floor section of roof, rolls to the gutter and dramatically plunges to the ground where he is tackled by uniformed police.
Police say specialist officers and negotiators had been speaking with the knife-wielding man when he fell.
He was treated by paramedics for stab wounds to his chest before being taken to Tamworth Base Hospital, where he remains under police guard in a serious but stable condition.
The critically injured man found inside the house was also taken to Tamworth Base Hospital but declared dead on arrival.
Police say the two men were known to each other.
A crime scene has been established as local detectives investigate the incident, assisted by the Homicide Squad.
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