Kiwi billionaire Graeme Hart has offered to buy one of the country's biggest food manufacturing firms, according to a filing with the NZ Companies Office.

Hansells Food Group managing director Ross MacKenzie was not available for comment to the Herald on the purchase and there was "no comment" from Hart's Rank Group.

Hansells company's latest available financial statements show the group posted a loss of about $6.7 million for the year to March 2017.

New Zealand's richest man Graeme Hart added $4.6 billion to his wealth in 2017.

The Hansells name has been part of New Zealand for 80 years. Hansells Food Group was created when Old Fashioned Foods acquired Hansells and the two company's brands were integrated.

Hansells was known for its essences and baking products as well as iconic New Zealand brands such as Vitafresh.

Old Fashioned Foods was behind the traditional steamed pudding brand Aunt Betty's, which began selling in 1996, according to the company's website.

The Companies Office website shows Hansells Food Group has been transferred to new shareholder HFC Acquisition Ltd - wholly owned entity of Hart's Rank Group.

The sole director of HFG is listed as Harrison Richard Francis Hart - understood to be Graeme Hart's son Harry.