There were reports of widespread 500 errors as well as Cloudflare Dashboard and API failing.
Thousands of users reported issues with a host of different websites including ChatGPT, film review site Letterboxd, multiplayer games such as League of Legends, X, Grindr and the Scottish parliament affected by technical issues at the internet network services business.
The DownDetector monitoring site, which was itself hit by the outage, showed a flurry of reported issues on Tuesday evening AEDT on Tuesday.
More than 10,000 DownDetector users reported issues related to Cloudflare.
Downdetector tracks outages by collating status reports from a number of sources.
Since the numbers are based on user-submitted reports, the actual number of affected users may vary.
"We saw a spike in unusual traffic to one of Cloudflare's services beginning at 11:20 UTC. That caused some traffic passing through Cloudflare's network to experience errors," the company said in an emailed statement.
"We are all hands on deck to make sure all traffic is served without errors."
A number of the websites affected, including X, came back online temporarily before suffering further problems.
Users saw a message on a number of the websites saying the issues were caused by an "internal server error on Cloudflare's network".
Cloudflare provides network and security services for many online businesses in order to help their websites and applications operate.
The company said in a server update that it was "experiencing an internal service degradation" and that some service may be intermittently affected.
It added: "We are seeing services recover, but customers may continue to observe higher-than-normal error rates as we continue remediation efforts."
Cloudflare, which runs services such as checking that visitors to websites are humans rather than bots, says about a fifth of all global websites use some of its services.
Cloudflare had scheduled maintenance for the SCL (Santiago) data centre for Tuesday.
Some cybersecurity experts have warned for years about the potentially ugly consequences of allowing a handful of big tech companies to underpin the online world's plumbing.
The Cloudflare outage is the latest to hit internet services.
Microsoft's Azure had also faced an issue last month while disruption at Amazon AWS caused global turmoil among thousands of websites and some of the most popular apps, such as Snapchat and Reddit, earlier in October.
with AP and Reuters
