The foul-mouthed Philippine president has vowed never to curse again - after "hearing a voice from God".

Rodrigo Duterte famously called the Pope a "son of a bitch" and told Barack Obama to "go to hell".

But the leader claims to have changed his ways after a experiencing an epiphany on a flight home from Japan.

Duterte said he was looking at the sky while everyone was sound asleep "snoring".

Then he heard a voice that said: "If you don't stop epithets, I will bring this plane down now.

"And I said, 'Who is this?' So, of course, 'it's God,'" he said.

"So, I promise God to ... not express slang, cuss words and everything. So you guys hear me right always because (a) promise to God is a promise to the Filipino people."

Duterte's vow was met with applause, but he cautioned: "Don't clap too much or else this may get derailed."