THE room is crammed with Chinese workers stripped to the waist. Poorly paid and exhausted from their punishing shifts, they chain-smoke and rub their eyes, while their colleagues sleep two to a mat on the floor.

But this Shanghai sweatshop is not churning out T-shirts, trainers or children’s toys. Its workers are known in the computer games world as “gold farmers”. They are playing online games and winning virtual gold, which the owners of the gold farms then sell on to cash-rich, time-poor Westerners for real money.

Ge Jin, a PhD student at the University of California in San Diego, has filmed these scenes for a forthcoming documentary on the economics of internet gaming. He believes that hundreds of thousands of people in China are now dependent on gold farming for their income.

The gold farmers spend most of their waking hours in front of computer screens, immersed in complex, three-dimensional virtual worlds known as massively multiplayer online games (MMOGs).

With an estimated 13 million paying users, this is one of the fastest growing areas of the internet. Millions of devotees play games such as Everquest, World of Warcraft (WoW) and Second Life around the clock. They build impossible palaces, slaughter hordes of monsters or simply hang out in virtual nightclubs and coffee bars.

In an environment where everything is created from digital pixels, the only limits to what a gamer can do is his or her imagination . . . or budget.

Everything is for sale, from better weapons to lap dances from Lycra-clad werewolfs. In some games, “in-game” currency is earned by setting up businesses that other players can then pay to use. Gold farmers tend to concentrate on violent games, where they become wealthy by defeating enemies and harvesting the spoils of victory.

By spending long hours in the game, they meet and vanquish more enemies or even the same enemy over and over. The “in-game” loot is then sold on for real money to players in the West over the internet. However, most gamers resent the farmers’ involvement because it disrupts the flow of the game and drives inflation for goods and services.

Blizzard Entertainment, which owns WoW, has shut thousands of suspected accounts, but the gold farmers are becoming increasingly brazen. Paul Younger, co-editor of worldofwar.net, said: “It’s getting ridiculous. They have started mugging other characters and stripping them of valuables. It’s meant to be a game, but when there’s money involved people will do anything.”

Professor Edward Castronova, an American specialist in MMOG economics, agrees that gold farmers are bad for gaming, but says they may enjoy better conditions than other sweatshop workers.

“When some lawyer’s kid has a more powerful character than mine just because daddy let him buy enough gold online to get him a set of über armour, that stinks for me as a normal game player. Everything I know about low-wage labour markets tells me that the wages they are making equal or exceed local market wages.

“Working in a room made safe for computers is going to offer better conditions than working behind a plough in some field.”