(Adds quotes, Beijing Olympic traffic curbs, paragraphs 11-16)

By George Chen

SHANGHAI, June 20 (Reuters) - Chinese motorists, knowing the price of petrol was about to jump, queued for hours at a gas station only to be told they could not be served until the price rise took effect, prompting angry scenes on the forecourt.

Word spread fast by phone and SMS after news of the price rise leaked out and soon motorists from around China's financial hub were heading to gas stations to fill their tanks.

Police were mobilised in Shanghai and government officials stood by at gas stations in Beijing, host of the Summer Olympics in just 49 days, to ward off any trouble from irate drivers.

At least one station told customers that it would shut for repairs until the price hike took effect at midnight, prompting an altercation between staff and angry motorists.

"You guys make a huge profit and get high prices. We consumers are pitiful," said a Shanghainese waiting to fill his Volkswagen Santana.

Prices for gasoline and diesel fuel rose unexpectedly by 1,000 yuan ($145) per tonne each effective from midnight on Thursday (1600 GMT). Beijing pledged subsidies to farmers and low-income families and taxi drivers to cushion the crunch.

"It's crazy," said another Shanghai man driving a Passat. "Inflation is becoming serious and harming my ordinary life -- I won't be able to stand it for long if prices continue to rise."

Most analysts had expected Beijing to hold out until after the Olympics in August as policymakers are anxious to avoid any hint of social unrest.

"I am wondering whether I need to forget my new car and take the subway to work as the cost of driving is too high," Zhu Hong, 28, who bought her car just two months ago, said.

PRICES DOUBLED SINCE 2003

The 16.7 percent increase in gasoline takes the pump rate to about 75 U.S. cents a litre, still a quarter cheaper than in the United States and about one-third what British motorists pay. Prices have doubled since 2003, but crude has more than quadrupled.

Taxi drivers were sceptical that promised subsidies would cover higher fuel costs.

"The subsidies are only symbolic. I guess they would increase the subsidy by 50 or 60 yuan (per month) after the hike," said Ding Shigen, a Beijing taxi driver for 15 years, who estimated his fuel bill would increase by over 1,000 yuan ($145) a month.

Beijing drivers will also be forced to leave their cars home on alternate days from July 20 to help ease congestion and reduce pollution during the Olympics and Paralympics.

Those affected by the odd-even number plate restrictions will not have to pay road or vehicle taxes for three months, a spokesman said on the city's official website.

Though unpopular with drivers, the petrol price hike would not spark social unrest ahead of the Olympics, mused one Beijing businessman surnamed Xu as he wiped his dusty van down with a cloth.

"Common people don't have cars. They'll welcome the decision as it hurts the rich," Xu said.

Analysts also ruled out the possibility of unrest even though inflation was a key factor behind the 1989 demonstrations centred on Beijing's Tiananmen Square.

"People are more able to tolerate price rises today than they were in 1989," Liu Xubuo, a dissident writer, said. "There won't be chaos."

Beijing taxi driver Fang Jinguan said there was no choice but to be philosophical.

"Whether you are willing to accept it or not, you have to accept it," he said. "The government is much stronger than its people." (Additional reporting by Ian Ransom, Michael Wei, Alfred Cang and Beijing newsroom; Writing by Nick Macfie; Editing by Alex Richardson)

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