Snapchat suffered a worldwide outage for at least four hours, prompting a flood of complaints on rival mobile application Twitter a day before posting its third quarterly earnings as a public company.
"We're aware of the issue and working on a fix," Snapchat said on its support Twitter account, recommending that users stay logged on.
- Snapchat's 'Snap Map': How to stay safe
- Snapchat shares for sale
- Snapchat captures Aussie's stage dives off four-metre balcony onto floor
Many users tweeted about being unable to sign on after logging off the app, which is popular among people under 30 for posting pictures that are automatically deleted within 24 hours.
Twitter user @bradleykeegan11 wrote, "(Snapchat) Won't let me log in and keeps saying 'could not connect'."
A spokesman for the Snap Inc unit did not immediately respond to a query about the size and cause of the outage.
Snapchat had at least a couple of technical issues in October, according to its Twitter support page.
Snap, which went public in May, is scheduled to report third quarter earnings on Tuesday.
Its stock closed down 2.8 per cent at $14.83 on Monday, below its initial public offering price of $17.