Detective Senior Sergeant Dene Begbie said police were at the dairy on Sunday about 15 minutes after the 111 call was logged with the police Northern Communication Centre.
"This matter is being taken seriously and is currently under investigation."
Mr Begbie said police had made an operational decision to not release footage of the robbery.
"We believe the offenders are very young and there has been criticism in the past of displaying footage of young offenders," he said.
The investigation into the first robbery on March 8 was still open, but police had not been able to identify those offenders.
On that occasion two men entered the shop and stole cash, cigarettes and other items, and appeared to be armed with a hammer or something similar.
In the latest robbery three men ran into Ye Korner Dairy and Takeaways in Crawford Crescent, Kamo, about 1.50pm on Sunday and demanded cash.
The trio grabbed biscuits, chocolates and chips before running off down Moehau Rd to Hodges Park.
The video clip shows a woman and her son behind the counter when the three men run in. One starts waving a crowbar at her and another man thrusts a knife at her.
A third person is crouching down and piling items into a bag.
The manager hopes by releasing the video, members of the public might be able to identify the trio and police can make an arrest before someone is seriously injured. The man said he was out the back of the shop with his father when he heard his wife yelling for help.
He had rushed through and tried to activate a panic button that could set off a loud alarm.
As he tried to do that, one man had dived across the counter and struck him on the head with a crowbar, leaving a cut behind his left ear, he said.
"I was just trying to protect my wife and son. It was terrifying and took only 25 seconds," said the man, who did not want to be named.
"We want these people caught before they really hurt someone. All the businesses being targeted are small - dairy owners, liquor stores and takeaways. We are not multimillion-dollar businesses. We are just making enough for our families," he said.
Mr Begbie said the victims of the recent robbery were fortunate to have not received more serious injuries "given the level of violence these offenders were prepared to inflict on them. A situation like that could have left them with more serious injuries, which could never be justified or excused".
"There's every chance there were more people involved or knew about the offending and have not come forward. We urge anyone with information on these robberies to call police (430 4500) or Crimestoppers (0800 555 111) to prevent more robberies from happening."