Asia will boast the world's two biggest casino markets as early as this year, with Singapore set to take the No. 2 spot from Las Vegas, a U.S. gambling industry group said Tuesday.

Frank Fahrenkopf, president of the American Gaming Association, said Singapore raked in $5.1 billion in gaming revenue last year and could bring in up to $6.4 billion this year. The city-state opened its first two casinos last year.

Las Vegas, which lost its No. 1 spot to Macau in 2006, earned $5.8 billion in casino revenue last year, but is a mature market with little potential for big growth.

Fahrenkopf made the prediction at the start of a gambling industry conference in Macau.

"It's going to be an extremely good year," in Singapore and Macau, he said. Casino revenue in Macau will probably grow 25 to 50 percent this year, Fahrenkopf said.

Gambling revenue in Macau, the world's most lucrative gambling market, hit $23.5 billion last year and monthly revenue has grown by at least 42 percent from February to May.

Fahrenkopf warned that Macau faces several problems that could put a damper on continued growth, including a labor shortage and lack of infrastructure as well as a government cap on the number of new gambling tables until 2013.

A possible crackdown on so-called junket operators could also limit expansion, he said. High-rollers from mainland China coming to Macau on junkets are a big source of cash for casinos, accounting in some cases for up to 70 percent of revenues.

Fahrenkopf said the government may change the way junkets operate, which would create uncertainty for casino companies in Macau that have stock listings in Hong Kong or the United States.

"One thing that investors don't like is uncertainty. The whole junket question and what's going to happen in the future creates uncertainty," he said.

Junket operators in Macau help facilitate travel by high-spending mainland Chinese to the former Portuguese colony and lend them money for their gambling. Debts are collected once the gamblers return to China.