SHANGHAI — International automakers are converging on China's commercial capital for a show that, once marginal, is now a key showcase - and battleground - for the world's only major growing car market.

The biennial Shanghai AutoShow, which opened Monday to media and today to the public, is expected to feature an unprecedented number of new vehicle debuts, reflecting the growing importance of this market for automakers.

It follows on the heels of Sunday's Formula One Grand Prix, another Shanghai event symbolizing the city's obsession with cars.

“The number of new launches, especially from global manufacturers, will set it apart,” says Paul Gao, CFO of Chery Quantum Auto Co., a new unit of Chery Automobile Co. that is developing upscale models for the domestic automaker. “Many automakers now see the Chinese market as at the forefront.”

Porsche started Sunday night by unveiling the Panamera, the German automaker's first foray into the luxury-sedan segment. Porsche said its decision to reveal the vehicle in China signals the rising importance of the country's auto market.

Porsche sales in Asia more than doubled in its 2007-08 fiscal year to 7,600 vehicles, the company said.

“This is a clear signal that we count on these markets and have full confidence in their future economic potential,” Porsche Chief Executive Wendelin Wiedeking said in a statement.

The new four-door Panamera will be built at Porsche's plant in Leipzig, Germany. It will enter the market in Europe, South America and parts of Asia in September, in North America and Australia in October and in China in early 2010.

China, the world's second-biggest car market, has revived sales after a late-2008 slump with tax cuts and rebates that are moving small vehicles out of showrooms nearly as fast as companies can make them.

Sales hit a monthly record of 1.11 million vehicles in March, exceeding U.S. sales for the third month in a row and up 5 percent from a year earlier.

The uptick in sales this year caught many automakers off-guard, since they had cut production in expectations that the slowdown in sales seen last year would persist in China, Gao says.

“There are supply shortages, and in some cases, automakers couldn't meet demand. Joint ventures rely on imported components, and many of the tier-one global suppliers were already on the verge of bankruptcy,” he said.

China is a lifeline for ailing General Motors Corp., which sold 137,004 vehicles in China in March, up 24.6 percent from a year earlier. Tax cuts and other government policies focused on encouraging sales of small, fuel-efficient cares pushed sales at its minivehicle joint venture, SAIC-GM-Wuling, up 38 percent to 90,784 vehicles.

Kevin Wale, president and managing director of the GM China Group, says GM intends to double its sales in China, to more than 2 million a year, by 2014. Among its strategies: introducing or upgrading more than 30 models over those five years.

It's a far cry from decades past, when vehicles like the VW Santana, a 1980s model made by Volkswagen AG's joint venture with Shanghai Automotive Industry Corp. were among the few choices on the market.

But both Chinese and foreign automakers now need a full portfolio, from the inexpensive compacts favored by first-time car buyers to the high-margin luxury models needed to compete with foreign-brand sedans.