"After five or 10 minutes, he selected a pair of earrings and I opened up the sliding door of the showcase and got them out. I told him I'd gift wrap them ... In doing so, I saw he had opened the sliding doors."
Mr Waterworth said it was his store policy for staff to relock the doors after dealing with the customer.
"I broke my own rule. As I was wrapping the gift, I noticed he was into the cabinet, loading things into what looked like a bag.
"At that point, I rushed around [the counter] but by that time he'd taken off and was heading out through the shop."
Mr Waterworth chased the thief out of the shop, but tripped as he pursued him.
"I fell rather heavily on the footpath. He was in quite a hurry, as you can imagine."
Mr Waterworth suffered facial injuries and stitches were inserted in his nose and mouth.
He is returning to hospital today for an x-ray as doctors believe he may have broken bones. "I'm finding it hard to talk, but other than that I think I'm pretty well."
His sister usually works in the store with him, but left early for the day just an hour before the thief struck.
Mr Waterworth said he didn't think twice about chasing him, but did not think about what could have happened until later.
"I've gone over everything in my mind and thought, 'Could I have done anything better?' But had I got hold of him, who knows - he could have had a weapon and I could be worse off."
He said the theft would not affect his going back to work.
"Believe it or not, the doctor has given me three days off ... so I'm going to give myself three days off."
The thief took off with a number of gold chains and bracelets. Mr Waterworth is not yet sure of exactly what was stolen.
He believes the man may have been watching the store and knew when he was there alone.
"It looks premeditated to me. I think he's probably been looking at the shop for a while and he knew our habits."
The thief was last seen running away from the store and police have told Mr Waterworth it's possible he got into a waiting vehicle.
They say that a dark-coloured, older-style hatchback with two males inside was seen in the area at the same time as the theft occurred, and have urged the occupants of the vehicle to come forward to assist with the investigation.
Mr Waterworth said he had received a lot of support from the people of Tawa.
"It makes me feel chuffed, really, that people care."