A neighbour said she heard screams from a house where a boy was arrested after his step-mother died from multiple stab wounds.

This morning, NSW Police arrested a 16-year-old boy in Woolooware, in Sydney's south and he was questioned at Sutherland Police Station.

The teenager was this afternoon charged with murder and refused bail to appear at a children's court today.

Emergency services were called to a house on the Kingsway about 1:30am and found the 42-year-old woman with multiple stab wounds.

Paramedics treated her at the scene before she was taken to Saint George Hospital, where she later died.

Neighbours expressed their shock and grief.

Payton Wilson said she was sleeping when she heard a woman scream.

"Probably lasted like 20 to 30 seconds, just of like obviously a woman, really high pitched, [it] sounded like she was in a lot of pain.

"There's a lot of yelling that comes from that house previously anyway, so I didn't think twice but I had no idea that was what was going down in there."

Another neighbour, Em Levy, broke down after learning about the stabbing from police.

She said she saw the woman on Sunday and described her as a "happy lady".

Acting Police Superintendent Steve Worthington said authorities were still trying to unravel the circumstances surrounding the stabbing.

"I'm unsure what sparked this we're just still investigating," he said.

"There's a crime scene been established at the premises at Woolooware, and that examination is still underway as well.

"All incidents that end up with persons with fatal injuries, doesn't matter where they take place, is upsetting for the community."

Police were door-knocking neighbours for information and will prepare a brief for the coroner.