Quezon City, the Philippines (CNN) It's monsoon season in the Philippines and in a ramshackle neighborhood in Quezon City, near Manila, a sudden downpour has left gray puddles in the rutted streets and fat, dirty drops of rainwater steadily dripping from corrugated metal roofs.

It's getting late as Leny Glivano, the neighborhood captain, a small woman with a zeal in her eye, coordinates with police Senior Superintendent Guillermo Eleazar. Together they go through a master list of suspected drug users in her barangay -- a Filipino word for neighborhood -- as they have done nightly for six weeks.

Soon, they are ducking down dark, narrow, trash-strewn alleyways into the heart of the Barangay Libis slum, accompanied by a slew of uniformed officers and as many as 10 helmeted, assault rifle-toting SWAT officers.

Officers and the neighborhood "captain" Leny Glivano talk to a resident of Barangay Libis during a late night visit.

'Knock and plead'

They're on a "tokhang," or "knock and plead" operation -- a tactic adopted from new President Rodrigo Duterte 's hometown of Davao City, where he was mayor for more than two decades.

The United Nations last week condemned Duterte's violent crackdown on drugs since he assumed office in late June, urging the Philippines government "to protect all persons from targeted killings and extrajudicial executions."

"Knock and plead" involves going to the homes of those suspected of using shabu -- the local name for methamphetamine -- and, with practiced, almost comically overwrought politeness, inviting those inside to accompany the police to the barangay hall.

"You're on our list," Eleazar says to one, who seems disoriented by the visible show of force at his front door.

"When was the last time you used?"

It's been a long time, the dazed occupant says. He's wearing shorts and holds a thin, grubby tank top as he blinks in the light.

"We'd like to invite you to the barangay for some clarifications," Eleazar says. The man meekly complies. The armed entourage moves on to the next address on the list.

Photos: 'Knock and plead': Persuading Quezon City drug users to register A Quezon City SWAT officer holds a shotgun during a "knock and plead" operation, as part of President Rodrigo Duterte's war on drugs. Police officers knock on doors to ask drug users to voluntarily surrender. Hide Caption 1 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register An armed officer accompanies a "knock and plead" operation in the Bangaray Labis slum in Quezon City. Hide Caption 2 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register Officers and the neighborhood "captain" Leny Glivano talk to a resident during a late night visit. Hide Caption 3 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register The "knock and plead" operations involve going to the homes of those suspected of using methamphetamine -- and inviting those inside to accompany the police to the local town hall. Hide Caption 4 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register At the hall, those rounded up sit around a starkly lit room, waiting to be registered as drug users. They are interviewed by police about local dealers. Hide Caption 5 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register Hands raised, the detainees recite a pledge that affirms that their surrender is voluntary. They promise to "undertake to stop all" drug-related activities. Hide Caption 6 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register Mug shots are taken, and those surrendering are required to provide a urine sample for drug testing. Hide Caption 7 of 8 Photos: 'Knock and plead': Persuading Quezon City drug users to register The detainees are also fingerprinted -- but the Philippines National Police Chief, Ronald Dela Rosa, tells CNN that the surrenders are not arrests. Hide Caption 8 of 8

Registration, mug shots -- and ice cream

At the hall, those rounded up sit around a starkly lit room, waiting to be registered as drug users.

There's around 10 of them this night. They listen to a short orientation speech by Glivano while rubbing their heads and looking at the floor.

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There's disbelieving laughter when she shows them a video of those who previously surrendered dancing in unison -- part of an ongoing local rehab program that includes counseling and regular checkups to ensure they stay clean.

One tells CNN he hasn't used shabu for weeks but suspected the cops would pay him a visit. He waited to surrender, hoping they would forget about him but, and under the watchful eye of Eleazar, insists he's happy to be here.

"It's time for a new life," he says.

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The surrender process involves signing an affidavit before undergoing interviews with police about local dealers. They then give a urine sample, get fingerprinted and are photographed.

Finally, hands raised, the members of the group recite, in halting English, a pledge that affirms that their surrender is voluntary. They promise to "undertake to stop all" drug-related activities.

Police then hand out ice cream and sodas.

An invitation or de facto arrest?

From the outside, the process smacks of an arrest (except for the ice cream). While the people on the list are invited to attend -- and the country's top police officer, Ronald Dela Rosa, tells CNN it is entirely voluntary -- few dare to decline.

Dela Rosa insists that those who turn themselves in aren't under arrest despite the mugshots, and the presence of an ink pad on the table at the neighborhood hall. He boasts there have been around 600,000 voluntary surrenders since the program went national.

There's a reason for his pride -- he initiated the program as Davao City's police chief before his meteoric rise to Philippine National Police chief under his old friend and colleague, Duterte.

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Climate of fear

The new administration enjoys high public approval ratings for its crackdown on drug crime, but not all are convinced.

"It doesn't sound like proper police procedure to me," says rights advocate Jose Manue Diokno, chairman of the Free Legal Assistance Group (FLAG). "These are in our view warrantless arrests."

There's "a new (climate) of fear in the Philippines," where suspects who don't have legal representation are made to sign documents incriminating themselves, Diokno says. The process, he says, is "a violation of our bill of rights."

There's no doubt it's a dangerous time to be involved in drugs in the Philippines. Since taking office in June, Duterte's time in office has seen over 1,900 deaths -- at least 756 killings of suspected drug offenders by police, and at least another 1160 unsolved killings, many drug related and many by suspected vigilantes, according to senate testimony by PNP police chief Dela Rosa.

"Law officials are acting as judge, jury and executioner," Diokno says.

With voluntary surrenders reaching well over half a million in just a few weeks, it's clear that Duterte and Dela Rosa consider the program a success. But the simple fact is, Eleazar laughs, those turning themselves in in Barangay Libis this rainy night are simply "scared to die."