Thousands of Kiwis unwittingly sampled its Burger Pizza, launched on June 21. (Representational)

New Zealand pizza chain, Hell Pizza on Friday denied misleading customers by covertly serving fake meat, despite a lawyer's warning that the company might have breached a trade act.

Thousands of Kiwis unwittingly sampled its Burger Pizza, launched on June 21, featuring a "medium rare burger patty" as a pizza topping, reports stuff.co.nz.

After selling thousands of the pizzas to customers around the country, Hell Pizza revealed on Wednesday that the patties were a plant-based meatless creation from US company Beyond Meat.

Beyond Meat uses ingredients that mimic the composition of real meat, like pea protein, coconut oil and potato starch, to create products that look and cook like beef.

Marketing lawyer Rae Nield said there was a high risk Hell was in breach of the Fair Trading Act, which protects consumers from being misled.

"What does a reasonable consumer expect if it says 'burger' and there's no qualifier - it doesn't say 'veggie' or 'meat-free'. A reasonable consumer is going to think that means meat," Nield said.

Although the company had since updated the pizza's ingredients list on its website to include "medium-rare Beyond Meat burger patty", Nield said it was still on questionable legal grounds, stuff.co.nz reported.

A spokesman for the Commerce Commission said on Friday it had received two complaints about the "burger patties" on Hell pizzas and they would be assessed as part of the commission's usual process.

Ben Cumming, General Manager of Hell Pizza, said although customers were told the patties were plant-based only if they asked, nobody had been misled.

The company assured there had been no breach of the Act.