Philippines President Rodrigo Duterte has expressed his support for same-sex marriage, after previously declaring his opposition, in an about-face that may displease bishops in the mainly Roman Catholic country.

Speaking at a gathering of LGBT people in his hometown Davao City, Mr Duterte vowed to protect the rights of homosexuals and invited them to nominate a representative to work in his government.

"I said I am for [same-]sex marriage if that is the trend of the modern times," he said.

"If that will add to your happiness, I am for it."

Mr Duterte previously was quoted by local media as saying he was opposed to same-sex unions because marriage in the Philippines is only between a man and a woman.

The President had brought up the gender issue in the past while attacking Western countries that allow it, especially those who criticise his brutal war on drugs.

Many countries, mostly in Western Europe and the Americas, have already recognised same-sex unions.

Australia is the latest to legalise it after federal Parliament earlier this month amended the Marriage Act to allow same-sex couples to wed. The first such marriages under Australian law were held on Saturday.

Catholic bishops in the Philippines, who also oppose Mr Duterte's bloody anti-narcotics campaign, have voiced concern over legalising same-sex marriage after his top ally in Congress vowed earlier this year to push for it.

"Why impose a morality that is no longer working and almost passed," Mr Duterte said, in an apparent reference to traditional church teaching on the issue.

"So I am with you."

He asked the LGBT community to nominate a representative whom he could appoint to a government post, saying he needed "the brightest" to replace those he had recently fired over allegations of corruption.

"You nominate somebody who is honest, hardworking. I give you until the second week of January to nominate," he said.

Reuters