US fast-food giant Burger King on Tuesday launched its meatless burger in Europe, hoping to capture a substantial slice of a growing market.

The vegetarian version of its prime "Whopper" hamburger is being added to the menu in 25 countries and 2,500 restaurants after testing in the United States and Sweden.

"It's the biggest production launch ever done in Europe. We see the potential in the future that this is a growing category," company president David Shear told AFP.

The new meatless sandwich is to be launched in Britain at a later date, possibly around the start of next year, the firm said.

Burger King, which is best known for flame-grilled patties, said with the new product it was now the biggest European fast-food restaurant chain offering a veggie burger.

The company said the vegetarian product had boosted sales of traditional burgers in the United States, as it attracted new customers who normally did not patronise fast-food outlets.

Some critics noted however that if the same cooking grills were used for meat and chicken products, strict vegetarians would shun the new offering.

Shear did not provide details on sales or European market targets, meanwhile.

The fast-food giant and competitors Yum Brands and Kentucky Fried Chicken have got a step ahead of McDonald's in the United States in recent months.

In April, McDonald's launched a test in Germany of its Big Vegan burger, developed in collaboration with Nestle.

Burger King has joined the list of fast food chains that offer meatless options with its vegetable-based burger
Burger King has joined the list of fast food chains that offer meatless options with its vegetable-based burger GETTY IMAGES NORTH AMERICA / Drew Angerer

It has also been testing a meat-free cheeseburger in Canada since late September but is not yet at the stage of large-scale sales.

The global food industry has seen competition open up for alternative proteins to draw in growing numbers of consumers who have adopted a vegan diet for dietary, ethical or environmental reasons.

JPMorgan has said the plant-based "meat" market could be worth $100 billion in the next 15 years because of the climate emergency, as beef production is a major global polluter.

British tycoon Richard Branson has invested in Impossible Foods, while Beyond Meat is part-financed by the billionaire philanthropist Bill Gates.

They are in competition with Dutch firm The Vegetarian Butcher, which was bought recently by the multinational group Unilever, and which supplies Burger King in Europe.

Nestle already has had a soya protein and wheat-based hamburger on sale in European and US supermarkets since the end of September.

Consultants Deloitte said in a recent study: "Gone are the days when plant-based alternative products were for the niche consumer and warranted limited shelf space...

"The European plant-based alternatives market leads the way in terms of market size, with the European meat substitutes market accounting for around 40 percent of the global market."

The market is forecast to grow to 2.4 billion euros ($2.6 billion, ?2.1 billion) by 2025 from 1.5 billion euros in 2018, it added.