Manny Pacquiao of the Philippines (R) lands a right against Floyd Mayweather, Jr. of the US in the fifth round during their welterweight WBO, WBC and WBA (Super) title fight in Las Vegas, Nevada, May 2, 2015. [Photo/Agencies]

Millions of Filipinos groaned in disappointment on Sunday as their national hero Manny Pacquiao lost to American rival Floyd Mayweather in the megabout.

The nation of 100 million people ground to a halt as most people stopped to watch Pacquiao. Filipinos filled parks, squares, gymnasiums, cinemas and bars across the nation to watch Pacquiao's 12-round battle with Mayweather in Las Vegas, which he lost in a unanimous points decision that many at home deemed unfair and disappointing.

Thousands of mostly poor people gathered in the main public square of Manila's Marikina suburb to watch the fight on a giant screen mounted on the back of a flat-bed truck.

In the southern port city of Zamboanga, loud boos echoed inside an army gymnasium where thousands of soldiers and their relatives also watched Pacquiao.

Pacquiao's rags-to-riches story, from high school dropout to millionaire world boxing champion in an unprecedented eight weight divisions, is a huge source of hope and pride in the Philippines.

Pacquiao is an "inspiration for every Filipino", President Benigno Aquino said in a statement before the fight.

Pacquiao, 36, leveraged his boxing popularity to get elected in parliament in 2010 and he has said he may run for president in the future.