Hui said none of the victims seen in the seized material appeared to be Hongkongers, but investigations were still under way.

Police in the five places seized more than 400 computers and external storage devices, along with 155 mobile phones, in raids between February 26 and March 29.

The 13 men arrested in the city included a teacher, chef, technician and retiree, according to police.

“[The teacher] worked in a school and was primarily responsible for management,” Hui said, adding the man had been suspended by his workplace following the arrest.

“As part of his tactics, the suspect allegedly took the initiative to approach children via social media platforms and gained their trust by chatting with them,” she said. “He then exploited their curiosity about sex and lured them into sharing nude photos of themselves to him.”

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The man was detained on suspicion of procuring people under the age of 18 to make child pornography – an offence punishable by up to 10 years in prison and a HK$3 million (US$383,200) fine.

The other 12 men, aged between 31 and 73, were accused of downloading and storing child pornography using peer-to-peer software.

They were arrested on suspicion of possessing child pornography, which is punishable by up to five years in jail and a HK$1 million fine.

A police spokesman said the other 259 suspects, aged from 12 to 70, were arrested in Singapore and South Korea over offences related to possessing or sharing child pornography. The 259 comprised 251 men and eight women.

The spokesman added that authorities in Australia and the UK provided intelligence in the joint operation.

A police source said the operation was the first involving authorities in the five places to combat child pornography.

“Police reiterate that the presence of child pornography materials only encourages paedophilia and related crimes. Possessing or sharing these materials indirectly supports their production,” the acting senior superintendent said.

Hong Kong police handled 63 child pornography cases last year, according to Senior Inspector Kwok Sze-wai of the force’s family conflict and sexual violence policy unit.

Out of the 63 cases, 44 involved children meeting perpetrators online, she said, adding they connected on social media, gaming platforms and instant messaging services.

She said 40 of the cases involved girls, nearly 70 per cent of whom were aged between 12 and 16.

Kwok said criminals would sometimes send their own nude photos to the underage targets to help them lower their guard and lure them into sharing explicit images.

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“In serious cases, once these criminals have obtained the victims’ naked pictures or videos, they will use these materials to threaten the victims, making them send more explicit images or forcing them to engage in further sexual activities,” she said.

The senior inspector revealed that some children sold their own nude photos to online acquaintances in exchange for virtual game weapons or money.

She said in one of the reports, a 13-year-old girl exchanged her nude photos for online game items worth dozens of Hong Kong dollars, and a 15-year-old girl in another case sold her naked images in exchange for money.

Acting Senior Superintendent Hui said the force would take stringent enforcement action to combat child pornography to prevent the exploitation and abuse of children worldwide.

She warned the public that “the internet is not a lawless realm”.

Hui also urged parents, teachers and social workers to remind children and students of the potential online dangers and traps.