Eight-time world boxing champion Manny Pacquiao has apologised after sparking a firestorm of criticism in the Philippines when he described gay couples as "worse than animals".

Key points: Manny Pacquio under fire for saying gay couples are "worse than animals"

Manny Pacquio under fire for saying gay couples are "worse than animals" Boxer has reinvented himself as a conservative politician and is running for the Philippines' senate

Boxer has reinvented himself as a conservative politician and is running for the Philippines' senate Critics says Pacquio is a "bigoted hypocrite" and a "blind prophet"

Nearing the end of a glorious decades-long boxing career, the 37-year-old is reinventing himself as a conservative Bible-bearing politician ahead of the country's May elections, when he is running for a senate seat.

"It's common sense. Do you see animals mating with the same sex? Animals are better because they can distinguish male from female," Pacquiao told local broadcaster TV5 in an interview aired earlier this week.

"If men mate with men and women mate with women they are worse than animals."

He later tweeted to followers that he was sorry for hurting people by comparing homosexuals to animals.

"Please forgive me for those I've hurt. God Bless!" he wrote.

Gay marriage is outlawed in the Philippines due to strong opposition from the Catholic Church.

Eighty per cent of the country's 100 million people subscribe to the faith.

Gay marriages are officiated at small churches but these unions are not recognised by the church or the state.

Singer Aiza Seguerra, who recently married her actress-girlfriend, called on voters to boycott Pacquiao, who is also preparing for his last boxing fight in April, calling him an "ignorant, bigoted hypocrite".

"You might have done our country proud but with your statement, you just showed the whole country why we shouldn't vote for you," Ms Seguerra said in a post on Instagram.

Last May, Pacquiao lost to American rival Floyd Mayweather in what was the richest fight in boxing history.

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The country's most popular gay comedian, Vice Ganda, tweeted: "Some people think they can judge people like God just because they've attended a prayer meeting and read the bible. The Senate needs experts on politics and law, not blind prophets."

Pacquiao gave the television interview as part of his campaign for one of 12 seats in the nationally-elected senate.

The most recent surveys suggest he would win.

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He currently represents his wife's impoverished home province of Sarangani in the House of Representatives and is notorious for his chronic absences, favouring boxing training over legislation.

In one of the rare times he spoke at the legislature, Pacquiao quoted heavily from the Bible as he vigorously sought to stop a proposed law, since passed, granting free condoms to the poor.

He credits his renewed Christian faith for transforming him from a free-spending womaniser and gambler into a devoted family man who can recite Bible verses.

"Outside the boxing ring, I don't think Manny Pacquiao should be taken seriously. It struck me first as funny. I pity him," Kakay Pamaran, a pastor at one of Manila gay churches, told Agence-France Presse.

"I would advise him to talk to more LGBT [lesbian gay bisexual and transgender] persons, meet them and not just reduce his concept of LGBT to the sexual act."

AFP