The HK$350 million is in addition to HK$370 million in illegal betting records seized in Hong Kong when officers busted a cross-border gambling syndicate in a joint operation with mainland police on June 8, days before the World Cup kicked off in Brazil.

Mainland police at the time also seized betting slips worth 320 million yuan (HK$397 million) for soccer matches and horse racing from the syndicate's base in Guangdong.

"The value of the bets and the number of arrests [in the past five weeks] have exceeded those in the previous World Cup tournament," a senior police officer said.

He added that the operation was ongoing and more arrests were expected before the end of the final between Argentina and Germany in Rio de Janeiro early tomorrow morning.

In the first four months of this year, raids on illegal bookies netted records showing they had taken HK$54.2 million worth of bets on soccer.

The HK$350 million in illegal bets found during the World Cup is 55 per cent more than the HK$225 million for the whole of last year. And it is a near threefold increase from the 2012 total.

A police source said bookmakers were working from a luxury hotel room, an illegal mahjong parlour, a restaurant and residential flats, taking online and telephone bets.

"Most of the illegal bets were placed via gambling websites that were registered in other countries," the source said.

Hong Kong police have been working with Macau and Guangdong authorities, as well as Interpol in eight Asian countries, as part of a task force during the month-long tournament to tackle illegal soccer betting.

In Macau, on June 19, police busted a bookmaking racket that allegedly took HK$5 billion in illegal bets on World Cup matches in a week. Four Hong Kong men were among 22 people arrested in the operation.

Gambling-related problems are believed to have led to at least three suicides in the city during the tournament. One of those was talented chef Lau Ka-lun, 30, who took his own life on June 19 by burning charcoal in his home in Fairview Park, Yuen Long, after reportedly racking up huge gambling debts. He was described as a master of culinary arts by the Department of Health and had been honoured by Le Cordon Bleu Institute of Culinary Arts.

Ben Li Cheuk-yan, executive director of Zion Social Service, which provides counselling for gambling addicts, said it had received more than 60 calls seeking help in June. That was 50 per cent more than it usually receives in a month, and most of the calls came from gamblers betting on soccer. He was expecting the total to be even higher this month.

"The situation is likely to worsen when the World Cup finishes. Gamblers are still placing bets on the final in the hope that they'll win back what they've lost," Li said, adding that they expected more people to seek help than in the last World Cup in 2010. Fifty-four calls came in June during the tournament that year.

The Caritas Addicted Gamblers Counselling Centre said it had received about 300 calls for help from gamblers or their families since the World Cup began, mostly related to soccer.