A woman in her 20s has died and a man is in custody, following a suspected stabbing in Perth's northern suburbs overnight. 

Emergency services were responding to a reported assault in Balga when the 22-year-old was found with serious stab wounds on Walderton Avenue just before 8pm on Saturday. 

Paramedics worked on the woman at the scene before she was taken under priority conditions to Royal Perth Hospital, where she later died. 

Less than 15 minutes after emergency services arrived, police located a 30-year-old man believed to be involved in the incident on the nearby street of Wittering Crescent. 

He was taken into custody, but no charges had been laid. 

Police said the victim was at the time with another woman, also aged in her 20s, who was believed to be known to the man. 

Forensic officers remained at the scene, near Balga Primary School. 

Takita Rance was at the scene on Sunday morning and said the woman was attacked while walking along the street. 

"They were just walking to go down to the other cousins' [house]," she said.

"That's when the man came out of that street right there and they tried to run because he came running towards them.

"[It's] crazy because I walk around the streets later than this, nothing has ever happened."

Lisa Rance said she saw the man in police custody after the incident. 

"He just smiled at us, we just got shivers down our spine."

WA Premier Roger Cook praised the work of emergency services. 

"Our thoughts go out to everyone that is impacted, families, friends," he said.

"These are horrible instances and I am very pleased that the police were able to be on the scene and have taken someone into custody."