Amazon customers are shopping at “record levels” worldwide this Prime Day, Amazon said Tuesday morning.

The 30-hour event had only just begun, and at 4 am ET Amazon said that millions of Prime members globally had already shopped the website for bargains and so-called lightning deals.

In the U.S., the Amazon Echo is the best-selling item so far on Prime Day, Amazon added. Other best-selling deals include those for Amazon’s Echo Dot, a 23andMe DNA test and Amazon’s Fire 7 Tablet with Alexa.

Amazon’s stock closed Monday, prior to Prime Day kicking off at 9 pm ET, up 1.8 percent. Shares were falling 0.3 percent Tuesday morning.

The shopping event, in its third year, is notorious for offering shoppers some of the best deals on Amazon’s own products. In 2016, Prime Day was the “biggest day ever” for Amazon devices globally and for each Amazon device category including the Fire TV, Fire tablets, Kindle e-readers and Alexa-enabled devices, Amazon said.

This year, new deals are hitting Amazon’s website as often as every five minutes and will be available to Prime members until midnight on July 11.

As of Tuesday morning, some products on Amazon.com had already sold out, with customers joining waiting lists as they scoured the best deals on everything from toothbrushes to laptops, Under Armour gear to trail mix.

Many of Amazon’s competitors, meanwhile, were seen hoping to capitalize on the heavier-than-normal online shopping traffic Tuesday, rolling out their own deals.

EBay, for example, had a banner on its website reading, “Their Prime Deal Is Our Everyday Deal.”