A gaming boom in the Philippines is attracting hordes of Chinese nationals to Manila's swankiest casinos, but hot on their heels are gangs that lure players into debt traps.

When the players cannot pay up, they are kidnapped by the gangs and their families made to pay a ransom.

"It's happening almost every other day. It's history repeating itself," Ms Teresita Ang-See, who led a crusade against local syndicates that preyed on wealthy Filipino-Chinese families in the late 1990s, told ABS-CBN News. Ms Ang-See is an academic and social activist who has written on issues affecting the Chinese communities in the Philippines.

Police data showed 23 Chinese nationals - all linked to gambling debts - were kidnapped last year, up from eight in 2017. As of February this year, eight had already been abducted.

In May, five Chinese were arrested for kidnapping three fellow Chinese. Last week, eight more were nabbed. They had been guarding eight gamblers rounded up from three casinos.

Ms Ang-See said the number of gamblers kidnapped could be five times higher. "The main problem is, very rarely do the victims file a case or pursue a case, even if already filed... In many of these cases, crime pays, and pays lucratively," she said.

Brigadier-General Glenn Dumlao, head of the police anti-kidnapping unit, told ABS-CBN News investigators had come across accounts where the victims signed waivers agreeing to be held until their families could pay the ransom, usually a higher sum than the gambling debt. "That's a voluntary act. If you look at the closed-circuit television camera footage, you don't see violence, restraint or a struggle."

While most of the victims were from China, some came from Hong Kong, Taiwan and Singapore. In 2017, the anti-kidnapping unit rescued a tourist from Singapore, Ms Wu Yan, from 14 men who had held her hostage inside a condominium unit after she failed to pay money lent to her as she gambled at a casino south of Manila.

Ms Wu was beaten and forced to appear in a video pleading with her family in Singapore to send US$180,000 (S$246,000) as ransom. But a guard at the condo chanced upon her as she managed to slip out through an unguarded door. It turned out that government agents were already at the building investigating another kidnapping - that of a Hong Konger who had also been taken from a casino.

Police later arrested 43 suspects, all Chinese nationals, except for two Malaysians. The same gang was behind two more abductions that year, with one victim coughing up 300,000 yuan (S$60,000).

Almost all abductions happened at the 1,000ha Entertainment City, a Las Vegas-style enclave just south of Manila. It has three integrated resorts run separately by Filipino billionaire Enrique Razon, Macau casino king Stanley Ho and Japanese gaming tycoon Kazuo Okada.

Malaysia's Genting is building its own resort there, while Hong Kong's Landing International Development is set to open its casino in 2022.

Loan sharks prowl casino floors, usually in teams of four, looking for vulnerable gamblers. They lend the gamblers money, taking a 10 per cent cut on the loan, and another 10 per cent if their targets start winning. If the player cannot pay up, they snatch him and take him to a safe house, usually a unit inside a guarded condo near the casinos. There, they torture and take a video of him begging his family to pay the ransom. One video seen by police showed a hostage with a gun pointed at his head.

At least one victim is known to have died. Mr Zhu Fang Mei was rescued in January and taken to a hospital but he died from his injuries.

Ms Ang-See said she has also received reports of Chinese gamblers choosing to die by suicide, out of shame.

Cases of kidnapping have gone up amid an influx of Chinese tourists and workers in the Philippines, as relations between Manila and Beijing have become warmer under China-friendly President Rodrigo Duterte.

The Philippines is being transformed by a massive surge in online gambling companies catering to players in China. Both online and offline gambling are illegal in China.

In the Philippines, the demand is expected to drive up gambling revenue to US$4.1 billion this year, from just over US$1 billion in 2016. Those figures include traditional casinos. The portion that flows back to the Philippines to pay salaries, rent, government bribes and other costs has given the economy a significant boost. The annual licensing fees - US$140 million last year, more than 11 times the 2016 total - are now the third-largest source of government revenue, behind taxes and Customs duties.

By some estimates, at least 100,000 people from China have moved to Manila to work for gambling companies as marketing agents, tech support specialists and engineers - all to serve the Mandarin-speaking clientele.

"Everybody is after the Chinese customer because they're the biggest market, and they're the biggest gamblers," said Ms Rosalind Wade, the Manila-based managing director of Asia Gaming Brief, a research and consulting firm.

In 2017, police were already tracking at least two loan-shark syndicates preying on Chinese casino players. Since then, more have been moving from across China as the Philippine pastures flourish even more.