World boxing icon Manny Pacquiao announced his retirement from what he called the "greatest sport in the world" on Wednesday to focus on a run for the Philippines presidency, the biggest fight of his career.

In a 14-minute video posted on Facebook and Twitter, "Pacman", as he is known in the sport, thanked fans worldwide before closing the curtain on a 26-year boxing career that earned him world titles in eight different divisions, which to this day remains unmatched.

"I just heard the final bell. Boxing is over," said the 42-year-old Pacquiao, now a Philippines senator, drawing a flood of reactions from fans ranging from disbelief to gratitude.

Pacquiao, whose fast footwork and blistering speed of punches made him one of the top offensive fighters in the sport's history, said he was at peace with his decision, adding it was the turn of other Filipino boxers to shine.

"As I hang up my boxing gloves, I would like to thank the whole world especially the Filipino people for supporting Manny Pacquiao," he said, fighting back tears.

Pacquiao came from impoverished beginnings as a ship stowaway who started fighting on the streets as a boy, with prizes of $2 a fight. His net worth was $63 million last year, according to his Philippines statement of assets.

He is widely rated as among the best pound-for-pound fighters in history, better than Muhammad Ali, veteran promoter Bob Arum said in 2010.

George "Ferocious" Kambosos Jr, an Australian world lightweight champion and sparring partner of Pacquiao, expressed his gratitude in a gweet, saying: "Thank you for everything you did for my Career #Legend."

'Greatest of all time'

In August, the father of five lost a WBA welterweight world title match against Cuban Yordenis Ugas, leaving his fight record at 62 wins, including 39 knockouts, eight losses and two draws.

"Manny Pacquiao will always be the greatest boxer of all time," said Senate President Vicente Sotto.

With his six-year term as a senator ending next year, Pacquiao this month presented himself as the best person to succeed President Rodrigo Duterte and lead the Southeast Asian nation of 110 million people.

While no one questions his prowess inside the ring, many political observers doubt his ability to fight entrenched poverty and social problems and handle the economic fallout and job losses from one of Asia's worst and longest-running COVID-19 epidemics.

"He is adored as a boxer, but even those who adore him as a boxer have second thoughts about his ability to govern," said Temario Rivera, a retired academic, citing his patchy Senate attendance.

Pacquiao has since 2010 divided his time between politics and big-money bouts mostly in the United States.

He promised to fight government corruption when he launched his presidential bid, remarks that further damaged his relationship with Duterte, whose bloody war on drugs and campaign to reintroduce the death penalty Pacquiao had wholeheartedly endorsed as a staunch loyalist.

Richard Heydarian, an author, columnist and academic who specialises in politics, said Pacquiao's retirement meant he will now give 100% to his political ambitions.

"I think Pacquiao is increasingly emerging as the candidate of the opposition," Heydarian said.

A new opinion poll showed Pacquiao rising a notch to fourth spot, cornering 12% of the 2,400 people surveyed, from 8% previously.