China will overtake the U.S. to become the world's biggest retail market in 2016, with estimated total sales of $4.886 trillion, compared with $4.823 trillion for the U.S., according to Emarketer. The New York-based research firm added that China will remain the world's largest retail e-commerce market, with sales forecast to be above $899.09 billion in 2015, representing 47 percent of global online retail sales. Online purchases will account for 18.4 percent of the country's total retail sales this year, the highest worldwide, and are likely to reach $2.416 trillion in 2020, according to Emarketer. The firm credited China's e-commerce boom to Alibaba, Tmall, and other Chinese online marketplaces that use their own payment systems to capitalize on rising incomes, increased internet access in rural areas, and a growing appetite for digital shopping.