At an event showing there is no age limit for critics of the president of the Philippines, hundreds of young students took to the street in front of their school Tuesday to slam the drug war in this Southeast Asian country.

Students from the all-girls Saint Scholastica College in Manila streamed out of their classes and marched to show opposition to Rodrigo Duterte's brutal campaign against drug dealers and users.

Christine Pinto, a Catholic nun at the school, told epa that almost 1,000 students aged 9-16 joined the protest, though only those who secured permission from their parents joined in.

"We encourage them to make a statement but of course we need their parents' permission. This institute has always been for social justice. For the truth, for freedom and that's what we teach to our students," she said.

Many students carried cardboard placards with messages such as "Youth Resist", "Stop the killings" and "EJK (extrajudicial killings) is not OK".

"We came to protest the extrajudicial killings and what's happening in our country," Yuki Abion, 14, told epa.

"I think that the fact we are normalizing killing is already a problem. That we think killing is normal. Killing is patriotic because he (Duterte) encourages us to kill drug pushers cause he doesn't consider them as people anymore," she added.

The peaceful march was a collaboration between the school, the Akbayan leftist party and Senator Riza Hontiveros, who is an alumni of Saint Scholastica.

Duterte, who was elected on a tough anti-crime platform, has faced wide-ranging criticism for his war on drugs, both from his compatriots and from foreign organizations.

Philippine government data released last month states that some 3,100 people linked to drug trafficking have been killed since Duterte took office on Jun. 30, 2016.

However, Human Rights Watch puts the figure much higher at more than 7,000, and attributes the higher number to vigilantes acting with impunity.

But Duterte remains popular among Filipinos, with the results of a Social Weather Stations (SWS) poll released on July 10 showing some 78 percent of Filipino adults approve of his performance.