A horrifying image of a schoolboy being dragged to a violent death in a dirty alleyway has galvanised the Philippines against a brutal state-led war on drugs that has killed over 12,500 people in the last year.

For a nation now largely immune to the bloodied corpses of alleged small time drugs users and dealers dumped on the streets, the graphic reports of the final moments of Kian Delos Santos, 17, who was allegedly shot three times by undercover police officers, have been too much to bear.

His killing last week has united the public, senior politicians and the Catholic Church into the most significant sweep of mass protests since President Rodrigo Duterte pushed for a savage crackdown on drugs after his election last June.

Most of the 12,500 casualties have been killed by masked assassins. An estimated 3,500 have been killed in police shoot-outs, which officers often claim were self-defence.