By Katie Hunt Business reporter, BBC News

Market bulls believe stock prices will continue to rise

The Chinese market has almost tripled in value this year as investors clamour for a slice of the world's fastest growing economy.

And if the shares of PetroChina soar when it lists in Shanghai next week, there's a chance the Chinese oil giant could become the world's most valuable quoted company, stealing the crown from ExxonMobil.

For some, this is a natural extension of China's economic rise.

For others, it's evidence of a massive stock market bubble that parallels the height of the dotcom boom.

Too hot?

China's market is displaying many of the classic warning signs of a bubble.

Cab drivers, college kids and Buddhist monks are making small fortunes in a frenzy of "chao gu" or stir frying stocks - Chinese slang for trading.

Internet chatrooms are abuzz with investment tips and reports say that millions of stock trading accounts are being opened each month.

People have a bullish feeling before the Olympics Professor Yao Shujie, China Policy Institute at the University of Nottingham

Investment guru Warren Buffett, who recently sold his Hong Kong-listed PetroChina shares for a huge profit, warned last week that China is too hot to buy.

By most conventional yardsticks, valuations of many of China's largest shares do look stretched.

China's main stock index trades at more than 50 times projected earnings of the companies listed on it, almost triple that of major European and US stock markets.

Different standards

Shanghai-based fund manager Chris Ruffle says China's market cannot be judged by the same standards as other exchanges.

Inflation exceeds the return on bank deposits and real estate has lost its appeal following measures taken by Chinese authorities.

Strict investment rules forbid Chinese households from putting their $2.3 trillion savings in overseas assets, leaving China's stock market the only option.

"If it was a normal market it would be overheated, but it's a closed system here," says Mr Ruffle, who manages a $3bn fund for Martin Currie, an investment management business with its headquarters in Edinburgh.

Mr Ruffle says that companies have enjoyed explosive profit growth of 30% in recent years and this could pick up pace as management techniques at state-run firms improve.

"Attitudes are changing. Managers regard themselves as executives rather than civil servants," says Mr Ruffle.

He plans to steer clear of big-name Chinese companies like PetroChina, but says he can still find good value firms in sectors such as healthcare, where the Chinese government is channelling investment.

Record listing

One factor behind the market's white-hot rally has been a slew of stock market listings. In the third quarter alone, China hosted 75 share offerings.

Many recent debuts have been household names in China and a big draw for local investors' cash.

BIGGEST FIRMS BY MARKET VALUE ExxonMobil PetroChina General Electric China Mobile ICBC Gazprom Sinopec AT&T BP China Life Source: Reuters

PetroChina, which is also listed in Hong Kong and New York, said this week it raised almost $9bn from its share sale, the largest amount raised in Shanghai to date.

"Prior to 2006, there were few big heavyweight firms listing in Shanghai," says Professor Yao Shujie, at Nottingham University's China Policy Institute.

"If prices continue to rocket when it's smaller firms doing [initial public offerings], to me that's a much clearer sign of a bubble."

Chinese authorities have taken some steps to cool the market but investors have so far paid little heed.

There is a strong conviction that the government will not allow a huge crash in share prices.

"People have a bullish feeling before the Olympics," says Professor Yao.

"They believe the government will do what it can support the market in case of difficulty therefore they are not so cautious about protecting their investments."

Political fallout

A crash would have political ramifications for China's leaders, who have staked their legitimacy on maintaining a breakneck pace of economic growth.

Ordinary urban Chinese would be the biggest victims of any crash, with foreign investment in the Shanghai market still subject to limits.

Stock ownership among ordinary Chinese is on the rise

"When it does fall it will be the middle classes marching on the streets," says Kerry Brown, associate fellow at international affairs think tank Chatham House.

"It would cause unease among those that have kept out of politics for the past two decades and dent confidence in the Communist Party's economic management."

The stock market boom has given China five of the world's 10 biggest companies by market value.