About nineteen thousand suspects have been arrested in a drive against organized-crime after a three-month operation in Hong Kong, Macau and Guangdong province, the BBC cited state media as saying.
The crimes involved include drug dealing, gambling and prostitution.
Reports said 4,343 people, 1,177 of them from mainland China, were arrested by police in Hong Kong, where more than 7,500 properties were searched.
In Hong Kong, police seized $102 million Hong Kong dollars ($13 million) in cash, along with drugs, pirated DVDs, weapons and contraband cigarettes worth HK$67 million.
In neighbouring Guangdong province, more than 11,000 suspects were arrested. And in Macau, almost 4,000 people were picked up by police.
The crime-sweep, part of a regular operation codenamed Thunderbolt 15, was reportedly the longest joint operation of its kind, and a model for increasing cross-border police cooperation in the future, state media said.