Online shoppers on Wednesday ordered more than 34 million items on Amazon Prime Day, making it a bigger sales day for the retailer than the biggest Black Friday in history.

Prime customers ordered 398 items per second during Wednesday's sale, which was held to mark the 20th birthday of Amazon.com. Prime members pay $99 a year and receive free two-day shipping, along with access to the company’s streaming music, videos and other services.

During the sale more users signed up to become Prime members than on any other single day, Amazon said.

“Worldwide order growth increased 266% over the same day last year and 18% more than Black Friday 2014 – all in an event exclusively available to Prime members,” said Greg Greeley, vice president of Amazon Prime, in a statement. “Going into this, we weren't sure whether Prime Day would be a one-time thing or if it would become an annual event. After yesterday’s results, we'll definitely be doing this again.”

Amazon wasn’t the only major retailer offering big sales. Retail rival Walmart wanted to get in on some of the media hubbub surrounding Amazon Prime Day and launched its own online sales this week.

Walmart said it was experiencing thousands of sales and reduced its threshold to receive free shipping from $50 to $35. The company did not respond to a request for comment on the sales event.

Amazon said that its sales Wednesday included:

56,000 sets of the Lord of the Rings: The Motion Picture Trilogy;

47,000 televisions, showing 1,300% year-over-year growth;

14,000 iRobot Roomba 595 Pet Vacuum Cleaning Robots,

12,000 copies of Fifty Shades of Grey unrated edition on Blu-Ray.

Black Friday is the day after Thanksgiving, which is generally considered to be the beginning of the holiday shopping season. It has increasingly become a critical day for retailers – and shoppers – as online and brick-and-mortar stores offer big sales to draw in customers.