Chinese police have arrested nearly 600 people in 22 provinces as part of their crackdown on gambling, the official China Daily newspaper reported.
Police raided two online gambling rings, one of them Taiwan-based, which they suspect may have handled bets worth as much as $60m (£32.1m).
Gambling is illegal in China, but is increasingly popular online and in casinos just across China's borders.
Border police have stepped up searches of travellers for illicit cash.
China launched its anti-gambling drive last week, after it emerged that a senior official had lost at least $300,000 in public money on trips to a North Korean casino. Cai Hao-wen has since gone on the run.
Mafia gangs
The arrests have expanded the scope of the crackdown to include online betting.
Police arrested 597 people involved with the Taiwan-based group, of whom 202 were gamblers and 395 were organisers, according to Tong Jianming, an official at the Ministry of Public Security quoted by China Daily.
Police seized 23m yuan ($2.8m; £1.5m) but the ministry believes the group and its mainland criminal gangs took bets totalling five times that sum in Beijing alone since May.