Blood-soaked, screaming children were found wandering the streets after a fatal stabbing in a Brisbane home overnight.

Police were called to Brompton St, in the southern Brisbane suburb of Alexandra Hills, shortly before midnight on Tuesday.

Inspector Rob Graham said the initial triple-0 call was about the dazed children wandering outside without an adult - with blood on them.

"That was the tragic call for service initially. Children walking around the street with blood on them. The first responding police turned up to a horrific scene," he told Channel 9.

Advertisement

When officers went inside the home they found two men "one dead the other almost dead", he said.

The children and the former wife witnessed the stabbing.

The dead man, aged 37, had recently began a relationship with the former wife of the second man, who was 39.

The former wife lived at the Brompton St home.

Police will allege the former husband fatally stabbed the younger man. The Nine Network reported he then inflicted serious stab wounds on himself.

"You can well imagine what the kids or the ex-partner have been through," Inspector Graham said.

A neighbour told the Today show she heard a man screaming "stay with your mother" before police and ambulance arrived.

A large crime scene has been established at the home.

The 39-year-old is being treated at Princess Alexandra Hospital.