Top evangelical leaders in the Philippines have condemned presidential hopeful Rodrigo Duterte's recent comments about a Christian missionary who was raped and murdered in the country in 1989.

Jacqueline Hamill was working in a prison in Davao City in the southern Philippines when she was held hostage, gang-raped and killed during a riot.

Duterte, who has been mayor of Davao for 22 years, recently referred to the incident at a rally. He said: "They raped all of the women... There was this Australian lay minister... when they took them out... I saw her face and I thought: 'Son of a bitch. what a pity'... they raped her, they all lined up. I was mad she was raped but she was so beautiful. I thought, the mayor should have been first."

A video of his remarks went viral over the weekend, and sparked mass condemnation.

He later apologised, saying in a statement: "There was no intention of disrespecting our women and those who have been victims of this horrible crime. Sometimes my mouth can get the better of me. My life is an open book. I am a man of many flaws and contradictions."

However, in a letter to Duterte, Bishop Noel Pantoja, national director of the Philippine Council of Evangelical Churches, and Bishop Efraim Tendero, secretary general of the World Evangelical Alliance, said they were "taken aback and aghast" that Hamill's death "became a laughing matter to your supporters and some of the viewing public".

Writing on behalf of 33,000 evangelical churches and millions of members, the two admitted that Davao has progressed under Duterte's leadership. However, they added: "With due respect, sir, your derogatory statement as an aspiring father of our beloved country about a woman victim of the heinous crimes of rape and murder in the performance of ministry work for the spiritual well-being of our people, while it may be an expression of utter anger or a joke, is an insult, is offensive and sacrilegious to her family, the Christian Church, the missionary-sending country and the mission society who saw her death as the ultimate sacrifice.

"We are not demanding apology or seeking retribution," the bishops continued. "We will leave it to your judgement on how you will respond to this letter in the listening ears and watchful eyes of millions of devoted followers of Jesus Christ in our country.

"Ultimately, all our actions and deeds will be weighed by God, but the public and the religious are concerned how you treat situations such as this and the way you handle yourself as a leader.

"While you claim to speak the language of the masses, as an aspiring President of our country, your comments, remarks, jokes and verbal expressions will be heard around the world as first representative of all Filipinos, as it has already been in this case. Whatever you say will bode well or ill for the country."

Duterte, 71, is currently the frontrunner in the race to replace current president Benigno Aquino III, who has been in office since 2010.

He has been criticised by human rights groups including Amnesty International and Human Rights Watch over his links to extrajudicial killings.

The election is scheduled to take place on May 9.