Man critical after Sydney building fire

A 50-year-old man is in a critical condition in hospital after a fire tore through his home in Sydney's northwest.

Emergency services were called to the blaze at a duplex on Stanley Street in Putney shortly before 4am on Saturday, which forced the evacuation of surrounding residents, police said.

One firefighter was treated for exhaustion and three neighbours for smoke inhalation, with all five patients taken to the nearby Concord Hospital.

The cause of the fire is not yet known.