The International Criminal Court's arrest warrant for former Philippine leader Rodrigo Duterte is "a massive success for victims," professor of international history Iva Vukusic said on Wednesday (March 12).

It was a big moment for the court itself, she added, as Duterte was expected to face charges over his bloody "war on drugs" at the ICC in The Hague, following his arrest in Manila on Tuesday (March 11).

"This is an opportunity for the court to show that it can deal with a big case and can have arrests and it can proceed as if things are, quote-unquote, normal."

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A plane carrying Duterte to the ICC took off for Rotterdam on Wednesday, after being delayed by a few hours during a layover in Dubai.

Duterte, who led the Philippines from 2016 to 2022, was arrested early on Tuesday in Manila, marking the biggest step yet in the ICC's probe into alleged crimes against humanity during an anti-drugs crackdown that killed thousands and drew condemnation around the world.

Duterte, 79, could become the first Asian former head of state to go on trial at the ICC in The Hague and according to Vukusic, this could be a first case dealing with "a situation that is not from sort of war or election-related violence."

The ICC's warrant for his arrest says that as president, Duterte created, funded and armed "death squads" in his war on drugs that carried out murders of purported drug users and dealers.

In coming days, he will be brought before a judge and will have the allegations read out in court. Prosecutors accuse him of crimes against humanity for systematic attacks that led to dozens of murders.

About 20 anti-Duterte protesters gathered on Wednesday outside the ICC with banners and a mask depicting him as a vampire. A handful of pro-Duterte protesters also gathered at the court building in The Hague.

The war on drugs was the signature campaign platform that swept the mercurial Duterte to power in 2016. During his six years in office, 6,200 suspects were killed during anti-drug operations, by the police's count.

Activists say the real toll was far greater, with many thousands more slum drug users gunned down in mysterious circumstances, some of whom were on community "watch lists" after they signed up for treatment.

"The arrest and surrender of Duterte before the International Criminal Court is the first step in the long way to justice," a lawyer representing the families, Gilbert Andres, said.

(Production: Ardee Napolitano, Tanya Wood)