Philippine President Rodrigo Duterte pledged on Monday to press ahead with a war on drugs that has already killed thousands, and castigated critics of his signature initiative.

Duterte opened his annual State of the Nation Address with a defence of the narcotics crackdown that is now in its third year and remains largely supported in the Philippines despite fierce international censure.

"Let me begin by putting it bluntly: the war against illegal drugs is far from over," he told hundreds of lawmakers, celebrities and dignitaries.

"It will be as relentless and chilling, if you will, as on the day it began."

Duterte launched the crackdown shortly after coming to power in June 2016. Since then authorities claim 4,354 alleged drug users and dealers have been killed in police operations.

However, human rights groups and critics say the true number of dead is at least triple that. They say the killing could amount to crimes against humanity.

"If you think that I can be dissuaded from continuing this fight because of demonstrations, your protests which I find misdirected, then you got it all wrong," he said, referring to critics.

"Your concern is human rights, mine is human lives," he added.

As Duterte spoke thousands of protesters took to the streets to denounce his administration's policies, including the drug war and a plan to re-write the constitution.

Demonstrators torched large effigies of the president and waved banners calling for wage rises and relief from rising inflation, hovering at a five-year high.

This year's address was also marked by high drama as political infighting in Congress delayed the passage of autonomy legislation for the nation's Muslim minority.

After years of political wrangling and negotiations, a final draft of the proposed law was on the point of being approved and sent to Duterte for his signature.

Never gain a foothold

But a fight for control of the top leadership post in the House of Representatives led to the delay of a final vote.

Duterte promised that the legislation would still move forward.

"When the approved version is transmitted and received by my office... I intend to - give me 48 hours - to sign it and ratify the law," he added.

The measure is the key missing element in a languishing peace pact with the largest Islamic rebel group, the Moro Islamic Liberation Front (MILF). Along with other guerrillas, it waged a rebellion that has claimed about 150,000 lives since the 1970s.

The law aims to reinforce a historic but fragile 2014 peace deal under which the MILF will give up its quest for an independent homeland in the southern island of Mindanao in return for self-rule in a newly declared autonomous region.

Both sides believe that creating the area will deter extremism in a region where brutal poverty and perennial bloodshed has fuelled recruitment by radical groups.

"I have made a pledge that ISIS (Islamic State) terrorists or groups or allies will never gain a foothold in our country," Duterte said, referring to the months-long siege last year of the southern city of Marawi by jihadists.

"We owe it to our fallen soldiers and police officers in Marawi and elsewhere to put an end to the bloodshed and seek the path of true peace." - AFP