Perched atop a cherry picker truck several stories high, Brazilian graffiti artist Eduardo Kobra sprays puffs of paint on a sprawling mural in the colors of the Olympic rings.

With three weeks to go to the Summer Games in Rio de Janeiro, Kobra and his assistants are racing to put the finishing touches on the 3,000-square-metre (32,000-square-foot) painting that graces a wall in the city's newly overhauled port district.

The mural depicts five indigenous faces representing the continents of the world, awash in the blue, yellow, black, green and red of the Olympics.

Thailand's Karen people represent Asia, the Huli of Papua New Guinea represent Oceania, the Tapajos of the Brazilian Amazon represent the Americas, the Chukchi of Siberia represent Europe and the Mursi of Ethiopia represent Africa.

"There is growing intolerance in the world," said Kobra, 40, of the motivation behind the work.

"Look at Europe, where people are rejecting refugees, rejecting what is different. I hope this mural, in the Olympic spirit, will help remind us that we are all different but all one: the human race."

Kobra and his team spent 15 days preparing the former shipyard wall by plugging its holes and painting it white.

For the past week, they have been working 11 hours a day to cover the wall -- about half the size of a football pitch -- in spray paint, acrylic and varnish.

They have already used 2,000 bottles of spray paint, 200 litres (50 gallons) of acrylic and 100 cans of varnish, says Kobra, who grew up tagging walls in a hardscrabble neighborhood of Sao Paulo called Campo Lindo.

From the age of 12 years old, "the street was my way to socialize, have fun and also protest against social exclusion," he said.

Today, he does graffiti "only with permission," he said.

His current work, called "We Are All One," is sponsored by the Rio 2016 organizing committee and city hall.

His goal is to finish it several days before the August 5 opening ceremony -- in time for the thousands of tourists and athletes expected to descend on the city's iconic waterfront.