AN unarmed man, accused of stealing a packet of biscuits, was tasered by at least three police officers before he collapsed and died on a Sydney street.

Graphic CCTV footage shows the man's final moments as he was chased down a city street by six officers and subdued by a final Taser shot, seemingly to his back.

The man, a South American on an expired visa, died on the spot, unable to be revived by the officers.

The Daily Telegraph has been told "at least three times officers used Tasers" on the shirtless robbery suspect.

Each time he recovered, fended off the officers and stumbled to his feet, until the final shot ended the incident.

Witnesses claimed the man screamed "help me" as the officers held him down.

Asked why the man was not simply crash-tackled or overpowered, senior police said officers were under the impression the man could have been armed. "He was tasered a number of times over a reasonable amount of time but he just kept going and was able to shove officers away," a police source said.

"The officers did not Taser him all at the one time. They tried to apprehend him but he was still able to push them away and keep running."

Police are now positive the man tasered on Pitt St is the same person that walked into a City Convenience store on nearby King St about 5.30am on Sunday morning and asked for someone to "help me" before stealing a packet of biscuits and fleeing.

Soon after, CCTV footage from the Coffee Pitt cafe on Pitt St, a 10-minute walk away, showed him being approached by at least five officers.

Footage from Sydney Council CCTV cameras is being studied to see what route he took and if he had a weapon and disposed of it. Toxicology tests will be carried out to see if drugs were in the man's system.

Workers at the convenience store who saw the CCTV footage said the man was rambling. "He came in once and then was told to get out. He came back about 10 minutes later and climbed over the security door and was inside the area where the attendant is suppose to be safe," one worker said.

"You can see him in the footage talking a lot. He said the world was going to end and to help him. He doesn't have a shirt on. He grabs a packet of biscuits before opening the door and going out."