Users say that they cannot sign into their accounts and are receiving incorrect password alerts.
eBay has said that it is aware of the technical glitch and working to resolve the issue.
This is the eleventh such outage eBay has suffered this year.
In a message posted on its announcement board, eBay wrote: “We are aware that some users may experience problems when using the eBay Site.
We are actively working on restoring the issue and apologise for any inconvenience caused.”
eBay administrators had earlier posted that the site was to undergo planned maintenance on 4 September.
Sellers and other users of the site took to eBay’s community forums and Twitter, where users were using the hashtag #ebaydown, to express displeasure.
“I am really frustrated. All my listings are gone!” wrote one user on the forum, with other sellers chiming in to report similar difficulties with listing pages and auction times.
“Think as eBay UK is down they should reimburse seller fees, how are we meant to sell anything,” wrote user @sammyholmes3.
Several other users have reported problems with PayPal, eBay’s payment processing site.
eBay’s websites have suffered a series of technical problems this year, in addition to a massive data breach in May which affected up to 145 million eBay customers.
Several US states as well as UK and European authorities are investigating the company in the wake of the breach.