Chau and 10 others were arrested by Macau police on Saturday, a day after after the mainland city of Wenzhou, a coastal city in Zhejiang province, issued an arrest warrant for the junket mogul, accusing him of operating gambling activities in mainland China.

In a press conference on Sunday, Macau police said they have received intelligence back in August 2019 saying there was an illegal gambling syndicate ran by a 47-year-old mastermind, who is a male businessman surnamed Chau.

They did not directly name Alvin Chau, but the Suncity Group chairman matches the mastermind's surname and age.

According to the intelligence, the syndicate made use of junket operations in Macau to set up an overseas betting platform targeting mainlanders. The illegal earnings were laundered via VIP gambling accounts and underground banks.

The case has been handled by a special unit since April last year. On Saturday, officers arrested the 11 in several flats inside a commercial building as well as in a residential flat for illegal gambling operations and money laundering.

The arrested admitted to establishing the overseas gambling platform, but refused to cooperate in revealing more details. Officers seized computers, servers, phones and 3 million Petacas (HK$2.9 million) in the operation.

Asked if the operation is related to Wenzhou's case, Macau police said it took the initiative in the investigation and collected intelligence from various law enforcers around the world.

Wenzhou authorities said on Friday their investigation had found that Chau formed a junket agent network in the mainland to help citizens engage in offshore and cross-border gambling activities.

Chau also set up an asset management company in the mainland to help gamblers make cross-border fund transfers, the Wenzhou City Public Security Bureau said on its Weibo account.

As of July 2020, the "crime syndicate" led by Chau had 199 shareholder-level agents, more than 12,000 gambling agents and over 80,000 punter members.

"The amount of money involved was exceptionally large, seriously damaging our country's social management order," the security bureau said.

Suncity operates VIP gambling rooms across Asia. Junket operators are go-betweens who bring high rollers to play at casinos, extending them credit and collecting on their debts.

Casino gambling is illegal in China outside Macau, the world's largest gambling hub.

In 2019 Suncity was singled out by state-backed Chinese media, which attacked online gambling for causing what it described as great harm to China's social economic order. Suncity said it did not operate any online gaming at the time.