UPDATE: A 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.

Police today defended the use of Tasers in the face of heavy criticism and concerns surrounding the death of the man early on Sunday in Sydney's CBD.

The man, who is believed to be South American, was stopped by officers investigating an incident at a convenience store. Police claim he resisted arrest and that they had to use capsicum spray and a Taser.

The man stopped breathing and could not be revived.

Police said they could not comment on reports that officers thought the man had stolen a packet of bisbuits from the convenience store.

Acting Commissioner Alan Clarke could not say how many times Tasers were fired or how many officers used their weapons.

"All those details will be dealt with in due course," he told ABC radio this morning.

"It's a complex investigation. There are number of avenues we need to look at."

The man's death has sparked renewed criticism about the use of the electroshock weapon, with the NSW Council for Civil Liberties calling for an immediate moratorium.

But Mr Clarke said people should not jump to conclusions.

"I think it is very presumptuous for anyone to determine the cause of death is a Taser simply because it's occurred in an incident where a Taser has been utilised," he said.

He said there were "very strict" guidelines surrounding the use of Tasers and that they were not used often.

"Amongst 16,000 police officers we are using the Taser less than once a day," he said.

"We couldn't say that every time we use a Taser it has saved us from using a firearm.

"(But) there's no doubt that police prefer to have an option less lethal than a firearm."

Police are yet to identify the dead man, who is described as being in his mid-20s to mid-30s, of medium build, 178cm tall, with brown eyes and brown shoulder-length curly hair.

He was wearing Diesel Industrie blue denim jeans and a white Gap brand short sleeved shirt.

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."

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

Tasers were introduced into the NSW police force in 2009.

In October 2010, a man died after being tasered by police during a domestic dispute in western Sydney and there have been deaths from the use of Tasers in other states.

Originally published as 'Tasered to death over a packet of biscuits'