U.S. online retail sales on Cyber Monday hit an all-time high and surpassed $1 billion for the first time for any single day of web shopping, according to research firm comScore Inc.

The S&P Retail Index was up 1.5 percent in the morning, and reach its highest intraday level since September 2007.

Amazon.com Inc and EBay Inc, which are expected to be among the biggest beneficiaries of robust online shopping, saw their shares rise. Amazon shares were up 1.6 percent, while EBay's gained 1.4 percent in morning trading.

Shoppers spent $1.028 billion online on Monday, 16 percent more than last year, comScore reported on Wednesday. Average spending per transaction rose 10 percent to $60.05, while the total number of transactions was up 6 percent to 17.1 million.

For the holiday season so far, online retail sales have hit $13.55 billion, up 13 percent from 2009, according to comScore.

ComScore expects online retail sales to rise 11 percent for the 2010 holiday season. It has raised its closely watched forecast twice.

The comScore figures echo those released on Tuesday by ChannelAdvisor and IBM Coremetrics that also found Cyber Monday online sales rose by double digits on a percentage basis this year.

E-commerce still makes up just a small percentage of the overall retail market, but online spending growth is outpacing that at brick-and-mortar stores, where sales gains are more modest.

Research firm ShopperTrak on Monday estimated sales over Black Friday weekend at physical stores were flat compared to last year, though shopper visits were up 2.8 percent.

The Monday after the U.S. Thanksgiving holiday was dubbed Cyber Monday five years ago to entice shoppers online. Originally, people returning to work after the break browsed for gifts on office computers, but the day has since attracted a wider group of shoppers.

(Reporting by Phil Wahba; editing by John Wallace and Derek Caney)