A man is fighting for life after he was allegedly stabbed in the chest and locked on the balcony of his Brisbane home while two children were also inside.
Neighbours and a jogger who was passing the house in Grange about 5.20am managed to rescue the children and tried to pull the man from the balcony before emergency services arrived.
A woman, believed to be the man's long-term partner, then allegedly locked the man on the balcony and set fire to items inside the house, including books and clothing.
She was arrested at the scene but has not been charged.
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Detective Superintendent Andrew Massingham said police believe the 44-year-old woman stabbed her 42-year-old partner in the chest with a 20cm serrated kitchen knife as he was having a cup of coffee on the balcony.
The stab wound just missed the man's heart, he said.
Police allege the woman then locked the man on the balcony and set fire to some items inside the house.
Massingham said two children, aged 11 and nine, woke to smoke alarms and were "quite distressed" as the front door was locked.
He said it was "extremely lucky" the jogger was passing the house at the time, and that neighbours also heard screams and called triple-zero.
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Witnesses were able to free the children before they sustained any injuries and used a ladder to get the man down from the balcony.
Firefighters arrived to find a curtain of fire inside the brick home.
The woman was found barricaded inside a bathroom. She was not injured.
The man was rushed to the Royal Brisbane and Women's Hospital, where he is undergoing surgery.
He is in a critical condition, but Massingham said he was conscious when he was being worked on by paramedics and gave some information about what happened.
The woman was given medical treatment and is now speaking with police.
Massingham said the children and witnesses faced a "sudden and horrendously graphic scene".
"Today is a tragedy," Massingham said.
"It's such a horrific event."
He said the house and people involved had not previously been known to police.
A neighbour of the home earlier told Today the incident is a shock for the "very quiet street".
"Nothing happens in this street," Tegan Sprenger said.
She said the young man who lived at the home had lived there for a while and seemed "like a nice guy".
Anyone with information about the incident is urged to contact police.
Support is available from the National Sexual Assault, Domestic Family Violence Counselling Service at 1800RESPECT (1800 737 732).
In an emergency, contact triple-zero (000).