By Caroline Bailey BBC News, Wuxue, China

Players can take time to build up virtual gold to buy their weapons

This is the online computer game economy where people assume characters and play to win virtual 'gold' which they can then spend in their game.

But to build up this credit can take hours, or even days - so around the world, some gamers are paying others to do the hard work for them.

It is estimated the market in buying and selling these virtual game items is already worth nearly $900m (£484.7m), and so-called "gold-farming" factories are springing up all over China.

Not surprisingly though, the companies making these games are unhappy that others are cashing in off the back of their online success.

Cyberspace business

In a scruffy apartment building down a muddy back alley in the provincial town of Wuxue in Hubei Province, one of China's newest industries is taking off.

The noise of computer generated monsters being slain in cyberspace rings out as twelve young Chinese men sit huddled over computer screens in a dingy room on the first floor.

All are playing the online computer game World of Warcraft - but not for fun.

This is their job.

Yes it is cheating in a way James Jones Online games player, Cardiff

The men here inhabit a fantasy world of role play with imaginary characters, and formidable monsters.

But what they're really doing is helping online game players worldwide to take a short cut, or cheat, depending on how you look at it.

Cash-rich, but time-poor players are paying companies in China for the virtual currency or 'gold' which is built-up by completing time consuming tasks. This helps them to get ahead with their own in-game character.

Overcoming virtual challenges is addictive but also time-consuming

The buyers are people like James Jones, a student from Cardiff who plays online computer games for up to twenty hours a week.

Recently he spent $25 of real money buying virtual gold from a website to use in his game.

Doing that saved him about thirty hours of playing time, he said.

The virtual gold was then used to pay for weapons, armour and clothes for his computer game character.

James accepts that this is not playing by the rules:

"Yes it is cheating in a way," he says.

"If you've got the time to make the money in game then all well and good. If you haven't then you're at a disadvantage aren't you?"

24-hour gaming

Back in Wuxue the men in this firm work ten to twelve hour shifts to provide virtual currency for players like James thousands of miles away.

The boss of the company Li Zhi explains how his 'gold farmers' work.

"Two people share a computer. They work eight to ten hours a day," he says.

"One plays during the day and one plays during the night. They swap shifts every two weeks. And they have one day off a week."

Across the landing from the computer room is a room with two large double beds. This is where the men who live too far away to go home, sleep between shifts.

They earn around $100 each month. Finding work in Wuxue is not easy and the men consider this to be a good job.

Virtual boom

There are ten other companies in this town doing the same thing and others are springing up all over China.

Some employ as many as 200 people to play games.

Online role-playing is increasingly popular around the world

Another man who has spotted a gap in the market is Alan Qui.

He has set up what he describes as an online stock exchange for virtual computer game currency.

His company, Ucdao.com, matches players who want to buy virtual currency with the working gamers, and he thinks there is great potential for China in this new business.

"What we have already started providing is a platform as seamless and efficient as a stock exchange. This is a budding and booming export industry for China," he said.

But the computer games manufacturers are not happy.

Whenever they discover a company generating virtual currency for buyer, they close down its accounts.