It was all over in mere minutes but as two people "stormed" dairy manager Rajat Sehdev, holding a knife to his neck, he felt like it was happening in slow motion.

Sehdev was about to close up Pleasant Heights Supermart on Sunday night when two people entered the store.

"It was immediately obvious they were trying to rob us. One of them had a hammer, the other one had a knife. They stormed me and held the knife to my neck, telling me to give them the smokes."

Sehdev said another worker was in the shop at the time and as they moved towards the counter, she pressed the button to deploy the fog cannon.

"It doesn't make a sound, it just fills the whole shop with thick fog. I don't think the people were expecting it because they just took off.

"It was only a couple minutes between them entering the shop and the fog cannon going off, but it felt like slow motion to me."

He said at the time it had crossed his mind that his life could be at risk.

"I think the fog cannon saved me. It was so helpful, it was a dangerous situation that could have ended with a very different outcome."

In February Police Minister Stuart Nash announced the Government would pick up the bulk of a $4000 price tag for a fog cannon in a bid to help reduce the number of robberies happening throughout the country.

The previous government set aside $1.8 million for the installation of devices such as audible alarms, fog cannons and DNA spray on a 50-50 cost share basis between the state and business.

However, Nash deemed the expected business contribution to be beyond the reach of many.

This is the first time Sehdev has used the cannon since installing it earlier this year.

"We were robbed in February so that's when we decided to get the fog cannon installed. It was expensive but worth it, I would recommend all dairy owners get one, even liquor stores would benefit from one."

Sehdev said his regular customers had been showing their support since the incident.

"Most of my customers are lovely. I had people coming in saying they saw the Daily Postarticle on Facebook and wanted to know I was okay."

Rotorua police area prevention manager Inspector Brendon Keenan said it was a positive outcome for the dairy owner.

No arrests have been made.

What is a fog cannon?
- A security device that fills rooms with dense fog in a matter of seconds. It is activated by an emergency button.
- It is made of a combination of glycol and water forced through a heated element. It is used in smoke machines and smells of peppermint.
- The fog is harmless to humans, animals, fixtures and IT gear.
- It clears in about 20 minutes in a well-ventilated room.