Macau is considering a system requiring travelers to declare the cash they carry across the border, according to a government agency that sets anti-money laundering guidelines.

The world’s largest gambling hub is studying a “cross- border cash declaration system, but no timeframe, declaration threshold or penalties are determined yet at the present stage,” Deborah Ng, director of the city’s Financial Intelligence Office, said in an e-mail today.

Visitors from China’s mainland have helped fuel a boom in Macau’s casinos, turning the city into the world’s largest gambling hub with $38 billion in revenue last year. Any controls imposed by Macau’s government would back China’s currency curbs, which restrict how much money Chinese tourists can take out of the country.

Travelers to Macau currently aren’t required to report how much cash they bring in when entering the city, said Daniel Tang, a press officer at the agency.

Tourists from mainland China can bring 20,000 yuan ($3,260) when traveling across the border and withdraw as much as 10,000 yuan a day with each card at cash machines. High stakes gamblers, who contribute about two thirds of the city’s casino revenue, rely on middlemen, called junket operators for credit to make big bets.

The use of outside VIP room operators by casino companies in Macau limits their ability to prevent money laundering and other illegal activities, one of Nevada’s top regulators said in testimony last month.

Criminal transactions “are widely alleged to take place just out of the direct purview of the casino,” A.G. Burnett, chairman of the Nevada State Gaming Control Board, said in testimony before the U.S.-China Economic and Security Review Commission in Washington in June.