CCTV from inside an Asian grocery store shows the moment a female shopper was knifed in the neck during Tuesday’s deadly stabbing rampage in Merrylands, Sydney.

The footage obtained by News Corp shows a man holding a knife and walking down the aisle of Bina’s Mini Mart towards the counter.

He approaches a 47-year-old woman who is standing there and strikes her in the neck. He strikes her again before leaving the store, reports The Daily Telegraph.

A worker rushes to the injured woman’s aid and applies pressure to her bleeding neck wound while waiting for emergency services to arrive.

Police said the woman was in a critical condition in hospital.

One man, aged 35, was killed and another man, 21, was injured in the random triple stabbing about 10am Tuesday.

The alleged attacker, aged 25, fled on foot but was arrested in a nearby street.

It has since emerged that the suspect had allegedly “absconded” from a mental facility 10 days before.

Western Sydney Local Health District said the man fled while being transferred from Cumberland Hospital to Westmead Hospital emergency department for further medical assessment on February 7.

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

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

The man has been charged with murder and two counts of cause wounding/grievous bodily harm to person with intent to murder.

He was refused bail to appear before Parramatta Local Court on Wednesday.

Forensics at the scene of the triple stabbing in Merrylands. Photo: AAP

Forensic police on Tuesday afternoon were seen entering and exiting a Nepalese grocer and a corridor leading to an accounting firm and training qualification organisation.

A knife about 25 centimetres long was used in the stabbings, Superintendent Simon Glasser said.

“The alleged offender is known to police for petty crime and a number of mental health incidents,” he said.

“He’s not linked to the address he was located. However, he is a local to the area.”

Early investigations suggested the victims were unrelated to one another, he said.

Police have not formally identified the dead man.

“As far as we’re aware at this point, there is no relationship between the three victims,” Glasser said.

“They were by themselves on Merrylands Road when this has occurred.”

The lethal incident would have been “highly confronting” for passers-by before lunch, when lots of people were on the shopping strip near the local train station.

Staff at a restaurant across the road from the scene said they didn’t see the attack but expected it would affect business in the area.

“It’s very quiet now … it’s going to affect a lot of our business because normally we have so many people coming for lunch,” the manager of the Kabul House Afghan restaurant said.

-with AAP