HONG KONG (Reuters) - MGM Mirage Inc , the world's No.2 casino operator, will open a 600-room, Las Vegas-style resort in Macau on Tuesday, raising the stakes in a Chinese gambling haven increasingly crowded by global players.

The $1.25 billion MGM Grand Macau, a joint venture between MGM and Pansy Ho, daughter of Macau gambling mogul and one-time monopoly holder Stanley Ho, is a relative latecomer to the once sleepy former Portuguese enclave, following Las Vegas Sands Corp (LVS.N: Quote, Profile, Research) and Wynn Resorts Ltd.

Foreign casino operators jumped at the opportunity when Stanley Ho's gaming monopoly expired in 2002, setting up giant Vegas-like facilities, replete with shopping arcades, entertainment complexes and vast casino floors.

Macau's economy has jumped, too, and annual visitor numbers have doubled since 2003 when the Chinese government began to loosen restrictions on individual travel for its population, with its legendary appetite for gambling.

Some 22 million people visited Macau last year, pumping its gambling revenues past those of the world-famous Las Vegas Strip.

The new resort targets high-margin high rollers -- the bread and butter of the gambling industry in the only place casinos are legal in China.

But questions hang over the sustainability of Macau's casino boom.

For one, Macau, with a population of around 500,000, will have to import huge numbers of workers.

Also, visitor numbers may be rising, but much of the new casino construction is betting guests will stay longer than the current average and do more than just gamble.

That may be a long bet, given that most of the gamblers are from China and have tended to spend the majority of their time at the tables.

Industry wide, VIP margins are declining as commissions rise with the competition, while on the mass-market side average revenue per table is declining.

MGM Mirage operates nearly 20 casinos, and in addition to the Macau offering it is developing a number of others, including the giant CityCenter project in Las Vegas and a $5 billion casino in Atlantic City.

The Financial Times reported on Tuesday that MGM Mirage was in discussion with Dubai World, holder of a 4.8 percent stake in the company, to extend their relationship into China, and was considering non-gaming ventures in Macau and China with its partners from the UAE. MGM Mirage had no immediate comment on the report.