Over 51,000 people suspected of links to criminal triads were arrested in a major cross-border sting in Hong Kong, Macau and China’s Guangdong province, state media reported Thursday.

In Hong Kong, 4,343 people, including 1,177 from the mainland were detained after over 7,500 locations, including vice dens, gambling venues and residential flats, were searched, the South China Morning Post (SCMP) reported. Authorities seized about HK$102 million ($13 million) in cash and HK$67 million ($8.6 million) in contraband, including illicit drugs, weapons, pirated media and cigarettes, in the three-month operation. 

In Guangdong province, over 11,000 people were arrested, and almost 4,000 were nabbed in Macau. In addition, 31,000 people described as “drug addicts” were rounded up across the three regions.

The authorities also uncovered evidence of criminal activities, including drug dealing, gambling, prostitution and parallel trading -- where traders take advantage of multiple entry visas to buy stock tax-free in Hong Kong before reselling it on the mainland -- Au Chin-chau, chief superintendent of the Hong Kong police’s Organized Crime and Triad Bureau said.

Au said that five major undercover operations were carried out during the sweep between June and September. Those arrested were mostly triad members from Hong Kong and mainland China -- including several high-ranking members.

"The message we want to send out to the public is that police have zero tolerance for organized crimes and any other illegal activities," Au said, according to the China Daily.

The massive sweep, which saw coordinated efforts between police departments, was part of an operation codenamed “Thunderbolt 15.” The sweep was delayed due to the massive Occupy Central protests that rocked Hong Kong from September to December last year.

The crackdown is a yearly mission to counteract organized crime activities. Au said the three-month sweep, which ended last week, was “successful.”

It came in response to intelligence, which suggested that triads operating out of Hong Kong and Macau have changed their tactics and started making forays into the mainland, in order to cooperate with local criminal elements and plan activities, a Guangdong police officer said.

The massive sweep comes after the arrests of 41 suspects, including one of the alleged leaders of the Wo Shing Wo triad, in May in a series of Hong Kong police raids.