More than $22bn has been spent online in the US since the beginning of November, 18 per cent up on last year, according to the latest market data.

Research firm comScore reported that online spending reached $881m on 10 December alone, up 33 per cent on last year.

This marked the heaviest online spending day of the season and the heaviest online spending day on record.

"The strong surge at the beginning of last week saw Monday and Tuesday easily surpassing $800m in sales and showing very strong growth rates, but the remainder of the week saw more modest spending," said comScore chairman Gian Fulgoni.

"However, we anticipate that spending at the beginning of this week will again be strong with most free shipping deals available until 18 December."

This year's 18 per cent online retail spending growth rate stands well below the 26 per cent rate at the same time last year.

An analysis of online spending by household income reveals that slower growth among lower income households is weighing on the overall season-to-date growth.

While households earning at least $100,000 have increased online spending 28 percent versus year ago, households making less than $50,000 have increased their spending by just 10 per cent.

"The current economic realities appear to be having a negative impact on the growth in consumer spending," explained Fulgoni.

"From the sub-prime housing meltdown to a decline in home values, to higher gas prices and an uncertain stock market, many consumers are either feeling the pinch or are lacking the confidence to spend at the rate they had in the past.

"Consumers in lower income segments appear to be the most affected, as evidenced by the sluggish growth in their rate of online spending."