BEIJING — As much of the world struggles to clamber out of a serious recession, a gradual flow of economic power from West to East has turned into a flood.

New high points, it seems, are reached daily. China has surged past the United States to become the world’s largest automobile market — in units, if not in dollars. It also surpassed Germany as the biggest exporter of manufactured goods, according to year-end trade data. World Bank estimates suggest that China — the world’s fifth-largest economy four years ago — will shortly overtake Japan to claim the No. 2 spot.

The shift of economic gravity to China has occurred partly because growth here remained robust even as the world’s developed economies suffered the steepest drop in trade and economic output in decades.

But that did not happen by chance: China’s decisive government intervention in the economy, combined with the defiant optimism of its companies and consumers, has propelled an economy that until recently had seemed tethered to the health of its major export markets, including the United States.

Yet China confronts a number of challenges about its recent surge, including whether its formula for growth is sustainable, and how it will manage its increasingly strained economic relations with the outside world.

Sustaining a global-size economy is not as simple as building one, some Chinese and Western economists say. As the Chinese navigate toward a bigger role in the world financial system, they are already running into diplomatic and political opposition.

At home, ordinary citizens and economists alike worry that the government’s decision to flood the economy with cash has created speculative bubbles — in housing, in lending — that could burst with disastrous effect. But curbing speculation requires moves, such as raising interest rates, that could crimp the sprees of investment and industrial expansion that are the main contributors to growth.

Abroad, the pressure on China to revalue its currency, the renminbi, is strengthening, and it seems sure to intensify after trade statistics showed that China’s yearlong downturn in export growth reversed in December. Keeping the renminbi fixed at a low rate against the dollar boosts China’s exports and its economy.

But increasingly, it angers its trade partners. China once could wave off complaints about its currency policies, arguing that it was a developing nation entitled to a period of indulgence from its Western customers.

But with the world’s fastest-growing economy — and more than $2 trillion in foreign reserves — that argument looks increasingly untenable.

“At a time when you’ve got 10 percent unemployment in the U.S. and a very slow and gradual global recovery — and China seems to be skyrocketing — the pressure on the Chinese to change some of these policies, including the exchange-rate policy, is really going to grow this year,” said Nicholas Consonery, a China analyst at Eurasia Group, a New York-based political risk research firm.

Not everyone is convinced that Beijing has eliminated threats to its financial and economic health.

Hit hard by an initial drop in exports, China poured $585 billion in stimulus money into its domestic economy. Officials also ordered state-run banks to increase their lending by double that amount, triggering a spree of easy money that created jobs for migrant factory workers and fueled rises in the price of assets, like stocks and real estate.

Some experts fear that too much of the stimulus money was put into unprofitable projects and bad loans that will be exposed in a few years. In that view, China’s 2009 boom, in which automakers sold nearly 14 million cars and trucks, and housing prices doubled, is a sign of an overheated economy at risk of serious recession down the road. Judged by the numbers, China’s economy still looks robust. In Beijing, officials said, per capita gross domestic product is expected to exceed $4,000 this year, a 10 percent jump from 2009.

Many experts see few signs of immediate danger. After all, they note, China has gone on splurges before — building too many steel mills, and too many office buildings — only to see the nation’s breakneck growth sop up the excess capacity. With nearly a billion people still clawing to advance beyond peasant status, they say, China’s growth story has many chapters ahead.

Scott Kennedy, who heads the Research Center for Chinese Politics and Business at Indiana University, said he was less certain that endless growth is such a panacea. “No one defies economic laws,” he said. “Eventually you get it, whether you want it or not.” (NYT)