Prime Day appears to be another big hit for Amazon.

The tech giant announced Wednesday sales for the two-day event, held Monday and Tuesday (July 15-16), were higher than sales during 2018's Black Friday and Cyber Monday combined.

Members worldwide purchased 175 million items during the two-day sale available only to subscribers of Amazon's Prime service.

In the U.S., the top sellers included the LifeStraw Personal Water Filter, the Instant Pot DUO60, and 23andMe Health + Ancestry kits.

Amazon also said its Prime Day event represented the two biggest days ever for new member signups.

Amazon started Prime Day in 2015 as a way to reward members of Prime, an annual subscription offering free shipping on thousands of items and access to services such as Prime Video. It costs $119 a year.

More:The 10 most popular Prime Day deals of 2019

This year, Amazon prefaced Prime Day with a live concert June 10 starring Taylor Swift. Last year, Ariana Grande headlined the event. Prime members can still watch the concert on Prime Video.

Amazon's event has grown big enough to attract competing retailers to launch their own sales alongside Prime Day.

Beyond Prime Day:These retailers are having major sales to compete with Amazon Prime Day

The event also drew attention to how well Amazon pays its employees. Workers in Minnesota walked out to protest conditions and wages.

Follow Brett Molina on Twitter: @brettmolina23.