There is outrage in the Philippines after a 17-year-old boy was shot dead in Manila, becoming one of at least 80 people killed this week in an escalation of President Rodrigo Duterte's ruthless war on drugs.

Philippines Duterte war on drugs
A rusty revolver is seen near the body of a man that police said had two sachets of Shabu or methampethamine chloride in his pockets Erik De Castro/Reuters

Police are under pressure to explain the circumstances surrounding the death of high-school student Kian Loyd Delos Santos.

Television channels aired CCTV footage that showed the boy being carried by two men to the place where his body was later found, raising doubt about an official report that said he was shot because he fired at police officers first. Witnesses told the ABS-CBN channel that the teenager did not have a firearm and police officers at the scene handed him a gun, asked him to fire the weapon and run.

National police chief Ronald dela Rosa said that if the Grade 11 student did not pose a threat, the officers who shot him would be held accountable. "Just think about it, he is just a kid. If that happened to your sibling?" he said on GMA TV. "We will investigate it, I assure you."

Philippines Duterte war on drugs
Policemen stand guard at the crime scene after three men were killed during a police anti-drug operations in Caloocan city, Metro Manila Erik De Castro/Reuters

Metro Manila police chief Oscar Albayalde said the three policemen involved had been relieved of their duties and an investigation would be launched into the incident, which took place in the Caloocan district in the northwest of the capital.

Police killed at least 13 people in Manila on the third night of a new push in Duterte's war on drugs and crime, taking the toll for the week so far to 80.

Earlier this week, 67 people were gunned down and more than 200 arrested in Manila and provinces adjoining the Philippines capital, in what police described as a "Oplan Galugad" (One-Time, Big-Time) push to curb drugs and street crimes. The term has been used by police to describe a coordinated drive in crime-prone districts, usually slums or low-income neighbourhoods, often with additional officers.

The spike in killings drew condemnation from Vice President Leni Robredo, from a party opposed to Duterte. Branding it "something to be outraged about", she has been a constant critic of the crackdown that has killed thousands of Filipinos and caused international alarm since Duterte took office over a year ago.

Several senators raised concerns over the rise in the number of deaths, calling for an impartial investigation. "Killing the poor and powerless is not the solution to the drug problem when tons of methamphetamine are smuggled in," Senator Francis Pangilinan said in a statement.

An ally of the president, Senator Jose Victor Ejercito, said he was "worried that these intensified killings are being used by some rogue police officers, knowing that the president will protect them". Police say there has been no instruction from higher authorities to step up their anti-drug operations and they are only doing their job.

Duterte indicated this week that the escalation had his blessing, saying it was good that 32 criminals had been killed in a province north of Manila and adding: "Let's kill another 32 every day. Maybe we can reduce what ails this country." On Thursday, he said he would not just pardon police officers who killed drug offenders during the anti-narcotics campaign, but also promote them.