Four decades after the Vietnam War ended, US fast-food giant McDonald's has opened its first restaurant in the country, aiming to lure a rising middle class away from rice and noodles.

McDonald's, one of the most potent symbols of US capitalism, arrived on Saturday in southern Ho Chi Minh City - known as Saigon when US troops dramatically withdrew in 1975.

The fast-food restaurant is following US rivals Burger King, KFC and coffee giant Starbucks into Vietnam - a country many Americans associate more with an unpopular war than a newly wealthy middle class.

But with its 90 million-strong population and average per capita income of more than $1,500, "Vietnam is on the radar now" for US franchises, said Sean Ngo, managing director of consulting firm Vietnam Franchises Ltd.

Critics say that Vietnam's rapid economic growth since "Doi Moi" reforms opened up the country in the early 1990s masks rising inequality and inefficiencies in an economy still dominated by state-owned enterprises.

But signs of the country's rising affluence were on display Saturday as hundreds of people lined up at the McDonald's restaurant on Ho Chi Minh City's Dien Bien Phu street - named after the battle that forced the French to withdraw from their former colony.

"I like fast food. I don't like Vietnamese food. I don't like fish sauce," Nguyen Hoang Long, 25, told AFP as he devoured a Big Mac, referring to the pungent condiment made from fermented fish and sea salt that is used liberally in local cooking.

A Big Mac costs about $2.85 at the new outlet, while a bowl of traditional pho noodle soup can be bought on most street corners for around $1.50.

The arrival of McDonald's marks a full turnaround for the fortunes of US brands in Vietnam.

Iconic brands such as Coca-Cola were available in US-allied South Vietnam until the end of the war, but the companies pulled out after the communist victory in 1975, which paved the way for the unification of the country in 1976.