Thirty-five-year-old Ronald Maskell, was stabbed in the shoulder and may have a punctured lung after the attack on Collins Street.

The Brighton man was opening a Hewlett-Packard service centre on Collins Street near the corner of Swanston Street when another man entered the second-floor office about 8.40am.

Mr Maskell approached the man, who was acting suspiciously and rummaging through a bag, and asked him, "Are you alright, mate?".

A tradesman standing nearby then intervened before Mr Maskell warned him that the man had a knife.

The unknown man, who a witness said appeared to be drug-affected, lunged at Mr Maskell four times, with one jab piercing his shoulder.

The offender then ran off, heading east on Collins Street.

Police have released CCTV footage and an image of a man they wish to speak to.

The footage shows a man walking past Phillippa's bakery in Howey Place, located at the rear of the shopping centre, about half an hour after the attack.

The man is described as being in his late 20s and about 180 centimetres tall with a tan complexion.

At the time of the stabbing, he was wearing a blue '80s style sports jacket, blue jeans and white runners.

Mr Maskell was taken to hospital with non-life threatening injuries. Doctors are investigating if he has a punctured lung.

According to his LinkedIn page, Mr Maskell was formerly chief concierge at Crown Towers and became manager of the Hewlett-Packard Experience Centre when it opened in March 2015.

Radio station 3AW reported that a worker from a nearby cafe saw police enter the building with guns drawn.

A source said there had long been concerns about security in the Collins Street building and that building management had received complaints.

"The exact circumstances are still being established, however police do not believe the pair are known to each other," a Victoria Police spokesperson said.

Hewlett-Packard spokesperson Luke Cuell said Mr Maskell was injured while attending to a customer.

"Our number one concern is for his wellbeing and he is receiving medical attention and is in good spirits," Mr Cuell said.

"We are working closely with the police investigation.

"While we are not aware of security reports, the wellbeing of staff is a primary concern and we are looking into the situation."

Many of the shocked shopkeepers at the building - Collins 234 Boutique Place - said they only found out about the stabbing after security guards told them.

The stabbing happened before many of the shops in the centre opened at 10am.

"Obviously nothing like that has happened in here before," said one shoe saleswoman.

The computer store put up a sign up saying the store was "temporarily out of service" until 12pm.

The offender remains on the run.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or make a confidential report at www.crimestoppersvic.com.au.

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