Cyber Monday sales were on course to bring in a record $9.4 billion, according to early estimates, building on a bumper Black Friday weekend for retailers driven by earlier-than-usual promotions and free shipping. 

Shoppers have already had nearly a month of special offers and deals as retailers look to draw out their vital holiday season, which is six days shorter this year due to a late Thanksgiving. 

Estimates from Adobe Analytics on Monday predicted that some $72.1 billion has been spent online in the past month, with Cyber Monday - now traditionally the U.S. economy's biggest internet shopping day - logging $473 million as of 9 a.m. ET. 

Amazon.com Inc and other traditional retailers such as Target Corp and Walmart have beefed up delivery services to fulfill online orders faster as more customers shop on their mobile phones and tablets at home.