BENGALURU (REUTERS) - Cyber Monday was on track to bring in a record US$7.9 billion (S$10.86 billion) in US online sales, as millions of shoppers scoured for steep discounts on everything from Lego sets to big-screen TVs.

The marketing event was picking up steam on Monday evening as West Coast shoppers looked for deals after work and those on the East Coast made purchases before bedtime, according to Adobe Analytics, which measures transactions from 80 of the top 100 US retailers.

A late evening forecast from Adobe estimated sales would be US$100 million more than it had expected earlier in the day.

"Many shoppers have waited on certain purchases, with three hours tonight expected to bring in as much revenue as an average full day," said Taylor Schreiner, director of Adobe Digital Insights.

Target Corp and Amazon.com were pulling out all the stops, offering free delivery with no minimum order requirement and bombarding shoppers with promotional e-mails.

Companies' sales were up 20 per cent from a year earlier as of 7pm ET, including a surge in orders placed via mobile phones, Adobe Analytics found.

On Wall Street, investors showed their enthusiasm. Shares of Amazon closed up 5 per cent. Macy's Inc, Kohls Corp and Target shares rose as well.

In another estimate, Mastercard SpendingPulse forecast a 25 per cent jump in e-commerce sales to at least US$3 billion, based on sales via the Mastercard payments network and estimates for other payment forms such as cash and check.

These US forecasts still paled in comparison to Alibaba Group Holding's "Singles Day" earlier this month, when the Chinese e-commerce giant raked in US$30.7 billion in sales.

Some industry observers saw a downside to the US shopping frenzy.

Bob Phibbs, chief executive of New York-based consultancy the Retail Doctor, warned of potential store closures if brick-and-mortar players discounted items too heavily this holiday season.

"Online discounts and free shipping are significantly cutting into retailers' profits," he said. "Retailers are just spending money in the hopes that they don't lose too much more."

The promotional efforts also drew the ire of customers who complained they woke up to even more Cyber Monday e-mails than in years past.

"Yes retailers, I'm aware it's Cyber Monday even without the 150 emails," tweeted Keina (@RealMamaEagle), a user from Delaware.

DEEP DISCOUNTS ON TOYS

Drawing an estimated 75 million shoppers, the day was a test of retailers' online platforms and delivery operations.

Without the right IT infrastructure, the heavy traffic could have caused hours of glitches like those during Amazon's Prime Day marketing event in July.

But as of 10:00pm ET on Monday, no big US chain had notable technical difficulties, according to outage tracker DownDetector.com. On Black Friday some websites including apparel retailer J Crew and home improvement chain Lowe's had temporary outages.

Consumers are increasingly doing their holiday shopping online, diluting the importance of Black Friday, when shoppers traditionally flocked to brick-and-mortar stores for the best deals.

Adobe said the nationwide average shopping basket was US$138 so far for Cyber Monday, up 6 per cent from last year.

"I find Cyber Monday to be more convenient than Black Friday," said Jeissy Casilla, 23, a retail worker in Puerto Rico. "I think that Cyber Monday is better in terms of how much you can get done while doing so little - basically a better chance at the best deals."

Toys were expected to have the biggest discounts, Adobe Analytics said, as retailers rush to fill the void left by the bankruptcy of top US toy retailer Toys "R" Us.

Target offered 30 per cent off on select toys, while Kohl's discounted Lego sets between 30 per cent and 40 per cent.

"This year, retailers are much clearer about where their strengths lie, rather than just attempting to beat Amazon at its own game," said retail analyst Carol Spieckerman.

The National Retail Federation forecast US holiday retail sales, including online, in November and December will increase between 4.3 per cent and 4.8 per cent over 2017, for a total of US$717.45 billion to US$720.89 billion.