GENEVA — Global retail e-commerce sales — spurred by big gains in China and other Asia-Pacific economies — are forecast to expand this year to $1.67 trillion, up nearly 25 percent from 2014, and account for a 7.3 percent share of the total retail market worldwide, research company eMarketer predicts.

The worldwide retail market is expected to expand this year by 6.3 percent to $22.8 trillion.

Between now and 2019, retail e-commerce sales growth “will continue to outpace brick-and-mortar sales growth by a more than 3-to-1 margin,” the research firm said.

As a result, eMarketer estimates e-commerce sales will grow to $3.5 trillion by 2019 and account for a 12.4 percent share of total retail sales worldwide of $28.8 trillion, with the Asia-Pacific the dominant growth market.

The outlook bodes well for online apparel sales, which rank among the top-five preferences for online purchases in regions such as the Asia-Pacific, North America and Europe, according to recent United Nations research findings.

The Asia-Pacific will be the main driving force behind the growth in online sales, the eMarketer study said, with sales in its e-commerce market growing faster than any other region, to reach nearly $875 billion, up 35.2 percent from 2014.

China alone is foreseen to account for more than three-fourths of spending in the Asia-Pacific region, with $672 billion, up 42.1 percent on last year’s sales of nearly $473 billion, and to represent about 15.9 percent share of the country’s total retail sales.

The huge gain in China’s sales, the report said, is expected to be driven by “digital buyers on mobile devices,” plus new digital buyers residing in rural areas. Nearly half of China’s sales this year will be generated by mobile devices, the research group said, predicting that by 2017, “China will become the first $1 trillion retail e-commerce market in the world.”

For India and Indonesia, the second and third most populous emerging markets in the region, the report estimates even faster growth in sales in 2015, albeit from a lower starting base, jumping by 80.3 percent to $11 billion, and by 65.6 percent to $3.2 billion, respectively.

Similarly, in North America and Western Europe, spending on retail e-commerce purchases is forecast to increase by 14.4 percent to nearly $376 billion, and by 12.7 percent to $313 billion, respectively, and with growth expected to come from “expanding online categories and increased order values.”

In the U.S., e-commerce sales will increase by 14.2 percent to reach $349 billion, or a 7.2 percent share of total retail sales. The study added that “though brick-and-mortar sales still command a vast majority of the market, e-commerce sales are increasing at a much faster rate.”

The study projects that by 2019, U.S. retail e-commerce sales will grow 57 percent to reach $548.2 billion.

Other findings by the report included:

• In 2015, more than 1.4 billion Internet users ages 14 and older will make at least one purchase via a digital channel.

• China has the world’s largest digital buyer audience with 407.6 million, followed by the U.S. with 171.8 million.

• The United Kingdom was the world’s third largest retail e-commerce with sales in 2015 projected to reach $99.4 billion, followed by Japan, $89.5 billion; Germany, $61.8 billion, and France, $42.6 billion.