Update, 3.25pm: Police are questioning a 24-year-old man over the stabbing death of an 18-year-old man in Noranda this morning.
Detective Sergeant Cameron Blaine from Mirrabooka police said the victim suffered a single stab wound to the chest following an altercation at a home on Widgee Road just before 11am.
The 24-year-old, who was known to the victim, was arrested a short time later at a home in Bedford.
The 18-year-old was taken to Royal Perth hospital where he was pronounced dead.
Forensics officers remain at the scene.
No charges have been laid. The victim's family has been notified.