Tributes poured in from across Latin America following the death of Uruguay's former president Jose "Pepe" Mujica, an ex-guerrilla fighter revered by the left for his humility and progressive politics.

The iconic 89-year-old – who spent a dozen years behind bars for revolutionary activity – lost his battle against cancer on Tuesday after announcing in January that the disease had spread and he would stop treatment.

"With deep sorrow, we announce the passing of our comrade Pepe Mujica. President, activist, guide and leader. We will miss you greatly, old friend," Uruguay President Yamandu Orsi posted on X.

"Pepe, eternal!" a cyclist shouted out minutes later, while passing government buildings.

Mujica earned the moniker "world's poorest president" during his 2010-2015 presidency for giving away much of his salary to charity and living a simple life on his farm, with his fellow ex-guerrilla wife and three-legged dog.

The government announced three days of national mourning and said his body would be taken to the legislative palace on Wednesday to lie in state.

Activists from Mujica's Movement of Popular Participation gathered outside the party's headquarters to make giant banners marked "Hasta siempre, viejo querido" (Until forever, old friend).

Leftist leaders from across Latin America and Europe paid tribute to the man described by Mexican President Claudia Sheinbaum as an "example for Latin America and the entire world."

Brazilian President Luiz Inacio Lula da Silva echoed that message.

"His human greatness transcended the borders of Uruguay and his presidential mandate. The wisdom of his words formed a true song of unity and fraternity for Latin America," Lula said.

In a 2012 interview, Mujica denied being poor, saying his was, rather, a life of "austerity."

"I need little to live," he said.

He transformed Uruguay, a prosperous country of 3.4 million people best known for football and ranching, into one of Latin America's most progressive societies.

In later life, he was disappointed at the authoritarian drift of some left-wing governments, accusing repressive leaders in Venezuela and Nicaragua of "messing things up."

He was diagnosed with cancer of the esophagus in May last year, and it spread to his liver.

Spanish Prime Minister Pedro Sanchez said Mujica had lived for "a better world," while Guatemala's Bernardo Arevalo held him up as "an example of humility and greatness."

Mujica is survived by his wife Topolansky. They had no children.

He asked to be buried on his farm, next to his dog. (AFP)