Now seven weeks into his presidency the carnage in the president's war on drugs has topped almost 1800, and the killings show no sign of abating as the island nation's system of governance is up-ended in a one-man revolution that has deeply upset the country's traditional ruling elite.

Human Rights Watch has called on Mr Duterte, the foul-mouthed former mayor of southern Davao city, to stop inciting violence which the New York-based organisation says should reap severe diplomatic and economic costs.

But opinion polls show Mr Duterte's approval rating hovering around 90 percent despite that since taking office he has threatened to seize additional powers through martial law, called the US ambassador of "son of a bitch" and homosexual, promised a hero's burial for the late corrupt dictator Ferdinand Marcos and complicated attempts by regional nations to preserve a common front against China's aggressive claim to the South China Sea.

Mr Duterte has also sacked appointed government officials and offered a pardon to former president Gloria Macapagal Arroyo, whose family was accused of corruption. But it is the so-called "war on drugs" that has alarmed human rights groups, the United Nations and the Catholic Church as the bodies have piled up, many of them killed execution style The extent of the carnage, which was revealed during a senate inquiry hearing on Monday and Tuesday, has renewed calls to end the killings.

Witnesses accused some policemen of gunning down suspects or being involved in illegal drugs.

Senator Leila de Lima, who heads the inquiry, said the campaign against drugs "seems to be an excuse for some law enforcers and other elements like vigilantes to commit murder with impunity." But national police chief Ronald Dela Rosa defended police, saying they had shot dead 712 drugs dealers after coming under fire since July 1 – the day after Mr Duterte took office. He said a further 1067 people had been killed by vigilantes, blaming the deaths on drug syndicates, which he claimed were being investigated by police.

"I admit many are dying but our campaign, now… we have momentum," he said.

Senator Antonio Trillanes told the inquiry that anarchy had arrived on streets of cities, towns and villages.

He warned that policemen who commit extrajudicial killings may eventually be held liable even though Mr Duterte has said he will defend them if they were fighting crime.

"President Duterte is in position now but what if his successor will prioritise human rights and conduct investigations?" he said.

Mr Duterte, who has said there will be no let-up in his relentless campaign, threatened to withdraw from the United Nations after UN human rights experts expressed concerns about the killings. But Philippine foreign secretary Perfecto Yasay played down the comments, saying the Philippines would never quit the UN and that the comments reflected the president's disappointment over the criticism.

The inquiry has heard a dozen witnesses testify about the killings of mostly petty drug users.

The Philippine Human Rights Commission said autopsies carried on and a man and his son showed they had suffered broken limbs before being shot three times.

"There was torture," said commission regional chair Gilbert Boiser.

The inquiry is being held amid acrimony, after Mr Duterte accused Senator de Lima, a former justice secretary, of being an "immoral woman" who had allegedly received kick-backs from drugs dealers. Senator de Lima denied the allegations and said the president was seeking to intimidate his critics and prevent scrutiny of the crackdown.

with agencies