Trash-talking Philippine presidential favourite Rodrigo Duterte has warned he is prepared to cut diplomatic ties with the United States and Australia after their ambassadors criticised his joke about the jailhouse rape of a missionary.

Duterte also told the ambassadors to ‘shut their mouths’, as controversy continued to rage over his comments in which he said he wanted to have been the first to rape the Australian woman who was brutalised and murdered in a 1989 prison riot.

‘If I become president, go ahead and sever (diplomatic ties),’ Duterte, 71, said on the campaign trail on Wednesday night, referring to the relationships with the United States and Australia, two of the Philippines' closest allies.

Duterte, who while campaigning has called the pope a ‘son of a bitch’ and promised to kill tens of thousands of criminals, recounted at a recent rally the riot events as part of his tough-on-crime pitch to voters.

‘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',’ he told the crowd.

‘I was mad she was raped but she was so beautiful. I thought, the mayor should have been first.’

Duterte was at the time mayor of Davao, a major city in the southern Philippines where he is accused of running vigilante death squads that have allegedly killed more than 1,000 people.

The front runner has at times on the campaign boasted about running the death squads, claiming they killed 1,700 people, but also denied any links to them.

Duterte has similarly offered varying responses to the rape comments, with his media team releasing a statement in which he apologised. But on the campaign trail, he has repeatedly told reporters he would not say sorry.

Australian ambassador Amanda Gorely criticised his remarks this week,  saying on Twitter: ‘Rape and murder should never be joked about or trivialised. Violence against women and girls is unacceptable anytime, anywhere’.

US ambassador Philip Goldberg later agreed with her.

‘Statements by anyone, anywhere that either degrade women or trivialise issues so serious as rape or murder are not ones that we condone,’ Goldberg said in an interview with CNN Philippines television.

- 'Shut your mouths' -

Duterte has repeatedly expressed anger at what he regards as their intervention in domestic politics.

‘It would do well with the American ambassador and the Australian ambassador to shut their mouths,’ Duterte told reporters on Wednesday.

A US embassy spokesman told AFP Thursday there was no immediate response to Duterte's remarks about the ambassadors. An Australian embassy spokeswoman said there would be no comment.

In another warning to the country's traditional allies, Duterte's camp signalled it was prepared to change foreign policy and start direct talks with China over a long-running territorial dispute.

President Benigno Aquino has been improving defence ties with the United States and Australia to bolster the Philippines in its dispute with China over the South China Sea.

China claims most of the South China Sea, even up to the coasts of its neighbours like the Philippines which has accused China of ‘bullying’ other claimants.

Aquino has refused to hold direct talks with China over the dispute, preferring multilateral discussions and filing a legal challenge with the United Nations.

However a Duterte spokesman said in an interview with ABS-CBN television on Thursday that he would be prepared to talk directly with China.

‘He is also supporting multilateral efforts to rein in China but at the same time, he is open to bilateral talks,’ said Peter Lavina.

‘He said, if we can talk to China (about) joint development of the resources of the South China Sea and eventually we need China's investments and technology.’