"We can confirm we have purchased the Mitre 10 site in Whangarei on the corner of Kamo Rd and Manse St," the spokeswoman said.
"The new store will replace our current store on Kensington Ave. At this early stage plans are still being finalised, but we will be working to bring a newer, larger and more modern Countdown store to Whangarei to open in the second quarter of next year.
"All of our team at Countdown Kensington have been offered roles as part of the move. In the meantime, the store will be operating as normal and continuing to serve our local community."
Mitre 10 moved out of the Regent site last year after it built a new Mitre 10 Mega store in Porowini Ave, leaving the Manse St site vacant.
Mitre 10 bought the site in October last year and it is believed to have then sold it directly to Progressive, via the law firm.
"We can confirm that we purchased three additional properties next to the Mitre 10 site," the Countdown spokeswoman said. "We are a tenant at the current store's [Kensington] site so once the new store opens this site will be vacated as our lease agreement will come to an end.
"We estimate the total investment of the [Mitre 10 site] project to be between $15 million and $18 million at this stage."
News of the sale comes after Progressive announced this week that work is expected to begin soon on the new, larger, $23 million Countdown supermarket in Dargaville.
A spokeswoman for Foodstuffs, which operates New World, said the company welcomed the competition from Countdown in Regent.
"We operate in a very competitive environment. We relish any competition, which is good for customers," she said.