Philippine President Rodrigo Duterte's office said "power naps" had caused the leader to miss key meetings at a Singapore summit

Philippine President Rodrigo Duterte brushed off claims of misogyny Wednesday after he kissed a Filipina woman on the lips onstage in Seoul -- saying they had both "enjoyed it".

The 73-year-old grandfather had offered a free book in exchange for a kiss during a trip to South Korea. He called a woman, Bea Kim, onto the platform during a speech on Sunday and pointed to his lips.

She initially hesitated, saying she had a husband, but later offered no protest as Duterte kissed her on the lips while the mostly Filipino crowd cheered and shrieked in apparent approval.

"We enjoyed it. It was a showbiz (thing) and everybody enjoyed it," Duterte told reporters upon his arrival back in Manila.

"I do not do it in public if there is malice."

Duterte even said he was willing to step down over the issue if complaints mounted.

"I think if all women here would sign a petition for me to resign, I will resign."

Since being elected in mid-2016, Duterte has caused uproar for his comments on women, including rape jokes, boasting about adultery, shaming female critics and inciting soldiers to shoot female guerillas in the vagina.

Women's groups and opposition lawmakers accused Duterte of abusing his position and misogyny following the latest incident, as footage of the kiss spread on social media.

The woman herself later told state-run Philippine media that there was "no malice" in the act, though Duterte critics said he had put her under pressure.

A defiant Duterte said the incident was "natural".

He said he had been kissing women on the lips in public for years, including when he was mayor of the southern city of Davao where he cast himself as a populist leader.

"That is my style. Find your own style. There is nothing wrong in a simple kiss -- you cause an uproar. They are just jealous," he said.

However the president, who has a daughter with his former wife and another with his current partner, said he expected them to confront him about the incident.

"You women, it's better if you just help me explain to them that it was just natural," Duterte said.