Philippine Senator Leila De Lima fights back tears as she speaks to reporters in Manila, on February 23, 2017

An arrest warrant was issued Thursday for the highest-profile opponent of Philippine President Rodrigo Duterte's deadly war on drugs, but she dodged police and sought refuge in the Senate.

The planned arrest of Senator Leila de Lima outraged her supporters and human rights activists, who said the government had manufactured drug trafficking charges to silence her criticism of Duterte and intimidate others.

The 57-year-old lawyer, who has spent nearly a decade trying to link Duterte to death squads that have allegedly killed thousands of people, could be jailed for life if she is found guilty of drug trafficking.

"I have no plans of fleeing and I have no plans to go in hiding. I will face all these charges," a tearful De Lima told reporters at the Senate in the early evening after a Manila court issued the arrest warrant.

De Lima then went to her home in another part of the capital after believing she had secured an agreement with authorities to surrender on Friday morning.

But, after police were seen on national television driving to her home to arrest her, De Lima quickly left and returned to the perceived safety of the Senate building.

De Lima appealed late on Thursday night for police not to arrest her overnight, and committed to surrendering on Friday.

"If they respect the Senate as an institution, they should not force an arrest tonight," she told reporters at the Senate.

Police followed her to the Senate. But, signalling an apparent pause to a night of intense drama, the head of security at the Senate and De Lima's aides said police had committed to waiting until Friday morning to arrest her.

- Political persecution -

De Lima is accused of orchestrating a drug trafficking ring when she was justice secretary in the previous administration of Benigno Aquino.

But De Lima and her supporters insist she is innocent, and that Duterte wants to crush one of his most vocal and enduring critics.

De Lima this week branded Duterte a "sociopathic serial killer" as she called for ordinary Filipinos to stand up in opposition to his drug war, which has seen more than 6,500 people killed since he took office eight months ago.

De Lima's Liberal Party, which ruled for six years under Aquino, voiced deep anger on Thursday at her imminent arrest.

"This arrest is purely political vendetta and has no place in (a) justice system that upholds the rule of law. This is condemnable. We reiterate that an arrest based on trumped-up charges is illegal," it said in a statement.

- Safety fears -

The party also said it feared for De Lima's life once she was arrested, citing the police killing of another politician, Rolando Espinosa, inside a jail cell in November last year after he was arrested on drug charges.

The National Bureau of Investigation said the police who raided the jail murdered him and that he was defenceless. But Duterte defended the police and vowed they would not be jailed.

Duterte, 71, won the presidential election last year after promising during the campaign to eradicate drugs in society by killing tens of thousands of people.

He immediately launched the crackdown after taking office in June and police have reported killing 2,555 drug suspects since then, with about 4,000 other people murdered in unexplained circumstances.

Amnesty International has warned that police actions in the drug war may amount to crimes against humanity.

Amnesty said Thursday that, if De Lima was arrested, it would regard her as a prisoner of conscience.

"The arrest of de Lima is a blatant attempt by the Philippine government to silence criticism of President Duterte and divert attention away from serious human rights violations in the 'war on drugs'," it said.

But Duterte's aides said De Lima's imminent arrest showed even the most powerful people would be brought to justice if they broke the law.

"The war on illegal drugs targets all who are involved and the arrest of an incumbent senator demonstrates the President’s strong resolve to fight pushers, peddlers and their protectors," presidential spokesman Ernesto Abella said.