Great White Southern Dive co-owner Pete Dryden said he had been down in the cage three times and had seen great white sharks each time.
Five of the massive fish swam around the 2m-high aluminium cage on his first dive, much to his amazement.
The experience of seeing sharks "with heads the size of the end of a 44-gallon-drum" close up was incredible, the former paua diver said.
"It's pretty awesome. It's something you can't describe. They're amazing."
Co-owner Peter Scott said since completion of the cage in January, it had been used by a Department of Conservation marine ecologist to tag great white sharks in the Southern Ocean.
It had also been used by NHNZ for 10 days to film a documentary on great whites.
Mr Scott said the $4500 cage had been tested extensively to make sure it would keep out the sharks.
He was now ready to take public ecotours in Foveaux Strait.
Cages used in South Africa and South America had taken a hammering from aggressive great whites, but Mr Scott said those living in southern waters were comparatively placid and inquisitive.
"I think it's because they are not hungry. There's plenty of food for them to eat around Stewart Island.
"Cages dropped in South Africa and South Australia have had their air hoses chomped through by the sharks. But our cage is indestructible because it sits just below the surface by the boat."
Sharks are lured near the cage by fish oil thrown into the water.
Mr Scott said when he first began the project, it was difficult to know whether it would work.
The biggest issue was what fish tourists would see, and how many tourists would want to see it, he said.
"The dives so far have produced pretty good results. They have exceeded our expectations."
Depending on the tours' popularity, members of the public could charter a dive in the cage for about $500 per person, per day, Mr Scott said.
The cage would hold up to four people at once: three tourists and one safety diver.
"Being up close and personal is a thrill. It's such a unique experience. You definitely wouldn't do it without a cage."
