An entire city police force in the Philippines has been fired in metropolitan Manila after some of its members were suspected in the gruesome killings of three teenagers and others were seen on surveillance cameras robbing a house.

The 1,200-strong Caloocan city police force will be relieved in batches and replaced, said metropolitan Manila police chief Oscar Albayalde.

The officers will undergo 45 days of retraining, after which those facing no charges can be reassigned to other stations.

The Department of Justice has started an investigation based on a murder and torture complaint against four Caloocan policemen allegedly linked to the killing of 17-year-old student Kian Delos Santos during an anti-drug raid last month.

The parents of two other teenagers - 19-year-old Carl Angelo Arnaiz and 14-year-old Reynaldo de Guzman - have also filed murder, torture and planting of evidence complaints against two Caloocan policemen.

Last week, security camera video purportedly showed 13 policemen robbing a house during an alleged drug raid.

President Rodrigo Duterte's crackdown on drugs, which has left thousands of suspects dead, has come under renewed scrutiny since police shot Delos Santos.

READ MORE: Thousands attend funeral for slain Philippine teenager

The death of the 17-year-old triggered rare public outrage over Duterte's so-called war on drugs.

Police described Delos Santos as a drug dealer who fired at officers during a raid, but his family and witnesses said the student was shot as he pleaded for his life.

Witnesses pointed to evidence, including a village security video, which they said showed two police officers dragging Delos Santos away shortly before shots rang out and he was found fatally shot in the head, holding a pistol with his left hand although his parent said he was right-handed.

Police officers testified at a Senate hearing that Delos Santos was not the man seen being dragged in the video, although several witnesses doubted the police statement.

Delos Santos's death was followed by another outcry over the killing of former University of the Philippines student Carl Angelo Arnaiz.

Police said he was killed when he shot it out with police after robbing a taxi driver last month. A government forensic expert, however, said Arnaiz apparently was handcuffed, tortured and shot five times.

Arnaiz's parents say he went out with de Guzman to buy a snack on the night of August 17 but never returned home. They found Arnaiz in a morgue 10 days later.

And Reynaldo de Guzman's body was found floating in a creek in a city north of Manila last week. The boy's head was wrapped with packing tape and his body bore about 28 stab wounds.

More than 50 children killed

Human Rights Watch, citing figures from the Children's Legal Rights and Development Center, estimated earlier this month that at least 54 children had been killed by police and "unidentified gunmen" in Duterte's war on drugs since July 2016.

The rights group said that "most of those children had been shot while in the company of adults who were the apparent target of the shooting".

It added that officials, including Duterte, "have dismissed those killings as 'collateral damage'."

The teen's killing puts focus on Duterte's repeated promises to police administering the crackdown that he would insulate them from any legal consequences. Critics say his rhetoric is tantamount to giving police a licence to kill.

READ MORE: Thousands tell Duterte - Stop killings in war on drugs

Activists have said that more than 13,000 people have been killed in Duterte's war on drugs.

Government figures said that 3,451 "drug personalities" had been killed in gun battles with police from June 30, 2016 to July 26, 2017.

Another 2,000 more died in drug-related homicides, including attacks by motorcycle-riding masked gunmen and other assaults, while 8,200 homicide cases are "under investigation", the data said.

Last month, Duterte took a softer tone on his drug crackdown, telling the police to arrest suspects and kill only if their lives were in danger. He said he would not protect those who killed unarmed people.

He added, though, that his crackdown on drugs will not stop.