China, already home to the world's largest online population, is likely to replace the United States as the biggest e-commerce market by 2015, according to new research.

China's e-commerce market is currently worth $74 billion -- less than half that of the United States at $177 billion, a new report by the Boston Consulting Group said.

But it is growing rapidly, spurred by increasing Internet use -- China now has an online population of more than half a billion -- the low cost of shipping and a passion for shopping among China's growing middle class.

"Consumerism is already big in China -- people simply love to shop. Beyond this, the Internet is affordable, and thus widely available," said the report, based on surveys of more than 4,000 online shoppers across the country.

"China... already has 145 million online shoppers, with exponential growth expected that could bring the number to 329 million by 2015 and make the e-commerce market in China the world's most valuable."

Within five years, online shoppers in China will be spending an average $980 per year -- twice what they spend today and close to the US average of $1,000, said the report, issued Tuesday.

Up to a quarter of e-commerce demand is for products consumers cannot find in physical stores -- a circumstance unique to China, whose huge size limits the coverage of physical retailers, it said.

The e-commerce industry benefits from China's low cost of shipping -- one dollar on average to ship a one-kilogramme parcel, versus six dollars in the United States, it said.

E-commerce in China will go from representing 3.3 percent of the country's total retail value today to 7.4 percent in 2015, an expansion that took the United States a decade to achieve, it added.