THE man who died after being tasered by police on one of Sydney's busiest streets may have lost his life over a packet of biscuits.

The victim was the suspect in a convenience store robbery, which had happened just minutes earlier, in which only biscuits were taken.

Just after 5.30am yesterday, police stopped a man on Pitt St in the CBD because he fitted the description of the suspect who had stolen something from City Convenience store on nearby King St.

After trying to subdue him with capsicum spray, a Taser gun was fired.

The man stopped breathing and, despite officers giving CPR, he could not be revived and died at the scene.

City Convenience store manager Sharif Al Ghazo said a man had entered the shop seeking protection from an individual or group of men.

When an employee in the shop refused to help him he fled, grabbing some biscuits on the way out.

"He said that the guy went inside the shop asking for help," Mr Al Ghazo said.

"He wanted to get away from someone who wanted to kill him.

"He did not want any money, he wanted protection. He took a packet of biscuits."

One Pitt St resident, who only wanted to be identified by his first name Dante, said he heard the sirens from his nearby unit.

He said he was woken by the commotion and went out to see what had happened.

"I didn't see him get tasered but the cops were giving CPR when I got here," Dante said.

"The cops were doing CPR for 10 minutes before the ambulance got here.

"There were maybe five or six of them helping."

The incident is being investigated by the homicide squad and the internal Professional Standards Command.

Police acting Assistant Commissioner Mark Walton would not say yesterday whether the dead man was armed or if he was under the influence of drugs or alcohol.

He said it was "unclear" as to how many times a Taser was deployed.

"The report of the robbery is the subject of further investigation and it's unclear as to the involvement of this man or the extent of that actual incident," he said.

"Whether it is a robbery or not is unclear at this time.

"The man who had contact with police and subsequently died has been identified through the description and the tracking using council's CCTV in an effort to identify and find that man."

The victim is yet to be formally identified by police.

Police believe he may have been from South America and have called for the public's help to identify him.

He was of medium build, 178cm tall, aged in his mid 20s to mid 30s, with brown eyes and brown shoulder-length curly hair, wearing blue Diesel Industrie jeans and a white Gap short-sleeve shirt.

It was the second incident involving a Taser in the city early yesterday, with another officer drawing, but not firing, his weapon to subdue a man involved in an altercation with a security guard in Oxford St, Darlinghurst.

The man was taken away by police but was not charged.

NSW Council for Civil Liberties president Cameron Murphy held serious concerns about the situations in which Tasers were deployed, police training and the fact they were being used in combination with capsicum spray.

He said yesterday's death was an "unacceptable result" and called for a moratorium and review of their use.

"They are dangerous and deadly weapons. It's not an alternative to the use of lethal force, they are lethal," he said.

Yesterday's death was the fifth stun gun-linked fatality in Australia since they were introduced. Premier Barry O'Farrell defended their use but would not comment on the incident directly.

"We've always supported the use of Tasers as a non-lethal alternative," he said.

"Tasers versus guns is a clear choice."

Originally published as Death by Taser over stolen biscuits