In a statement, the world's largest online retailer said many shoppers were ordering items successfully despite the glitch.
Trouble on the Amazon.com site spiked just as the event began at 3 p.m. Eastern time Monday, but declined significantly within a couple of hours.
Thousands of people also reported losing connections with their Alexa digital assistants via Echo voice-activated speakers and having trouble streaming Prime Video. Amazon Web Services, the company's cloud-computing division, reported global problems with its AWS Management Console, one of its tools.
Despite the issues, Amazon said Tuesday that sales in the first 10 hours grew at a faster pace than during the same period of 2017's event. It said it sold millions of devices that work on the Alexa voice-activated platform, with top-sellers including the Fire TV Stick streaming device and the Echo Dot speaker.
The problem is most likely a bug in a software update that should be fixed within hours.