Detective Sergeant George Staunton said a member of the public called police just before the robbery as he saw two young men preparing just outside the store.
Mr Staunton said within minutes police went to the scene and arrested two teenagers nearby. They were allegedly carrying money and alcohol.
He said the store worker suffered a serious head wound and was hospitalised overnight on Sunday. He was expected to be discharged last night.
Mr Staunton said the police wanted to thank the man who called police.
"The member of the public who saw something and did something needs to be acknowledged for making the effort to help and to have the trust and confidence in the police to respond. Two youths were in custody in four minutes of receiving his call.
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"The caller did the right thing to call police because what he initially saw did not sit well.
"This is an example of if you see something that's not right, it probably isn't, so well done to that member of the public of the picking up the phone and calling police."
The Bottle O store owners Charanjit and Ami Dhillon, who own six Bottle O stores - five in Rotorua and one in Tauranga - said they had just installed CCTV cameras in all their stores, costing a total of $32,000.
Mr Dhillon said each store was connected to the others, meaning all six stores could keep an eye on each other.
He said the Sunset Rd Bottle O owner noticed the robbery in progress on Sunday afternoon and also contacted the police immediately.
Mr Dhillon said the technology was so clear, you could "see an ant crawling on the carpet".
However, the Dhillons were furious they had to resort to such expensive equipment to keep themselves safe.
Mr Dhillon said he would like to "chop the hands off" the person who did this kind of thing.
"They tried to kill my staff member for a little amount of money."
He said his staff member was still shaken from what had happened and was nursing a wound on his head about 5cm long and 2.5cm deep.
Mr Dhillon said normally his stores had more than one staff member working but on this occasion the staff member was alone.
Mrs Dhillon said they were not the only store owners in New Zealand who were getting "angry and frustrated".
"People are working and providing a living for their families. People are going to be too scared to work soon because they don't want this sort of thing happening," she said.
"We are not some vigilante group but it's out of frustration and anger. If something like that happens and we retaliated, imagine what would happen then?"
She said she was thrilled with how Rotorua police had handled the situation.
"I would like to thank the Rotorua police . They are amazing. They need to have credit for that."
Meanwhile, police asked anyone with information to contact Detective Constable Rob Hutchins of the Rotorua CIB on (07) 348 0099.
Information can also be provided anonymously to the organisation Crimestoppers on 0800 555111.
