Vincent Go spends most nights on the road, waiting to hear where the next victim in Manila's drug war has been found.

For the past year, the photographer has been documenting the dead. One man, one camera — and the end of the lives of 300 men, women and children.

President Rodrigo Duterte has defended this so-called war on drugs, saying police are authorised to shoot only when threatened by suspects.

But human rights groups including Amnesty International have accused Philippine police officers of "systematically planning" the killings.

Warning: This story contains graphic images that some readers may find distressing.

Children in a slum in Navotas watch as mortuary workers retrieve a man's body. ( Supplied: Vincent Go )

Go works as a freelance photographer working for UCAN, the Catholic Church's newsagency in Asia.

"In the beginning, it was just journalistic work," he said.

"We just covered the killings — the killings that we thought would somehow stop because [the president] promised it was only for about three months."

Two men killed at a market in Navotas were fire victims living in a makeshift shelter. ( Supplied: Vincent Go )

But then Mr Duterte announced he would need more time, claiming the drug problem was bigger than he originally thought.

"Then it became six [months], then it's become over a year, and the killings are still continuing," Go said.

In Manila, the killers mostly strike at night. There were more than 12,000 deaths from July 2016 until May this year, according to figures released by the Philippine National Police.

A poster covers the body of a man who was shot while drinking with friends in Quezon City. ( Supplied: Vincent Go )

More than 3,500 have been attributed to deaths during police operations; the majority are categorised as deaths under investigation, attributed to vigilantes or gang killings, or unresolved.

Street slang has evolved to label these drug squad killings "EJKs", short for "extra-judicial killings".

"Tok-hang", which stands for "knock and plead", has also entered the language to describe the death knock on the door of a suspected drug user or trafficker.

Carlito Gatchalian, a meth user, was cornered in an alley and shot by four masked men. ( Supplied: Vincent Go )

"I really support the government campaign against illegal drugs — everybody supports it," Go said.

"But I don't believe this is the way you go about cleansing society of the drug menace.

"You don't just go around telling people that these are not humans and they deserve to die."

Leah Espiritu, 32, was shot while doing laundry, leaving behind her fiancé and six kids. ( Supplied: Vincent Go )

One of Go's photos is of the body of Leah Espiritu, a mother of six who was accused of being a small-time drug runner.

She was doing laundry in the street outside her home when two gunmen on motorbikes casually rode up and shot her in the head.

"We feel that documenting all these families is very important," Go said.

Rogelio Gilbuena, 56, was abducted by men in balaclavas who claimed to be police operatives. ( Supplied: Vincent Go )

"For the government, it's just statistics to them, it's just numbers. But [we want] to give faces to these numbers; we want to know who these people are.

"They are people. They are not just numbers."

Watch Ginny Stein's stories from Manila Wednesday and Thursday on Lateline at 9.30pm AEST on ABC News and 10.30pm on ABC TV. Listen to Background Briefing via podcast on Friday or on RN at 8am Sunday.