The brawl initially erupted between a group of men inside a Kmart in Mount Druitt Westfield at 5pm yesterday.

9News understands one of the men was stabbed inside the shopping centre. 

NSW Police said the brawl spilled outside the shopping centre at one point.

Police were called and arrived at the scene to find a man aged in his 20s with stab wounds to his upper body.

Emergency responders moved everyone to the back of the store and held them there while working to treat the man’s injuries.

Eventually, customers were let outside, with police snapping a picture of everyone’s ID to form a witness list. 

He was taken to Westmead Hospital with critical injuries.

A younger man, believed to be aged in his early teens, was treated for a slash wound to his hand and face.

He was taken to Nepean Hospital in a stable condition.

A third man in his 20s was treated for minor injuries.

Police believe everyone involved was known to each other, and suspect the offenders had already fled the scene before they arrived.

Police have established two crime scenes, one inside the Kmart and another on the external footpath.

Officers have seized several items of interest, including a butter knife.

No arrests have been made. 

Anyone with any information is urged to contact Crime Stoppers.