A man arrested after a fatal stabbing in Sydney’s west escaped from care while being transferred between hospitals for emergency treatment more than a week ago, health authorities say.

This morning, a man died and two people were critically injured in the attack in the middle of a busy Merrylands shopping strip.

Police arrested the man behind a nearby house on Smythe Street and took him to Granville Police Station.

A crime scene on a street, with police tape.

Investigators believe the Merrylands stabbing was a random attack. (ABC News: Berge Breiland)

Western Sydney Local Health District (WSLHD) has confirmed the same man escaped from care 10 days before the incident.

“The District is aware a person alleged to be involved in the incident is a recent patient of Cumberland Hospital, which provides acute inpatient care for people with complex mental health needs,” a spokesperson said in a statement.

Cumberland Hospital

The man is known to police for a number of mental health incidents, and was recently receiving treatment at Cumberland Hospital. (ABC News: Timothy Ailwood)

“On February 7 … this person absconded from care while being transferred from Cumberland Hospital to Westmead Hospital emergency department for further medical assessment.

“NSW Police were notified and contact was made with the patient’s family, but all attempts by WSLHD to contact the person were unsuccessful.

Exteriors of the Westmead Hospital Health Precinct in Sydney's west.

The man was being transferred to Westmead Hospital when he absconded. (ABC News: Jak Rowland)

“A formal review into the person’s care and treatment will be undertaken, which will include an external senior psychiatrist.”

The spokesperson said WSLHD expressed its sympathies to the families, victims and first responders impacted by the “confronting and deeply distressing incident”.

Alleged offender known to police

NSW Police Superintendent Simon Glasser earlier today said the alleged offender was known to police “for petty crime and a number of mental health incidents”.

It is believed a kitchen knife 20 to 30 centimetres long was used in the attack.

police lead a man whose face is blurred from a police car into a lockup.

The suspect was arrested and taken to Granville police station. (Supplied: NSW Police Force)

Two of the stabbings are alleged to have occurred inside a premises on Merryland Road, and a third on a footpath.

Superintendent Glasser said the incident was a “random attack” and there was no known relationship between the three victims.

“It’s a horrible offence to have taken place in Merrylands just prior to lunchtime with lots of people around,” Superintendent Glasser said of the “highly confronting” scene.

No charges have been laid over the incident.

‘Absolutely terrible’ scenesSeveral police vehicles pictures on street

First responders were met with a confronting scene. (ABC News)

Witnesses who contacted emergency services told the ABC of the “carnage” that confronted them at the scene.

“It’s absolutely terrible. In the middle of the day,” one man said.

“When I saw this, I just stopped immediately and just saw this carnage.”

Another man working nearby said he heard screaming before authorities arrived soon after.