"Twitter may not be working as expected for some of you. Sorry for the trouble. We're aware and working to get this fixed," the company tweeted from its "support" account.
The issues are affecting users around the world, including in Australia
Further details were unavailable Wednesday afternoon and an email seeking comment from the company's press account went unanswered.
Twitter has dissolved its media relations team.
Users first noticed the problem when they tried to send tweets and received a message saying they had reached their "tweet limit".
While Twitter has for years limited the number of tweets an account can send, it is 2400 per day, or 100 an hour - far more than most regular, human-run accounts send on the platform.
Accounts also had trouble when they tried to follow another Twitter user, getting a message "You are unable to follow more people at this time" with a link to the company's policy on follow limits.
Twitter's long-standing limit on how many accounts a single user can follow in a single day is 400 - again, more than a regular Twitter user would generally reach on any given day.
It is not clear what caused the meltdown but Twitter engineers and experts have been warning that the platform is at an increased risk of fraying since Musk fired most of the people who worked on keeping it running.
In November, engineers who left Twitter described for The Associated Press why they expect considerable unpleasantness for Twitter's more than 230 million users now that more than two-thirds of Twitter's pre-Musk core services engineers are apparently gone.
While they don't anticipate near-term collapse, the engineers said Twitter could get very rough at the edges - especially if Musk makes major changes without much off-platform testing.
One Twitter engineer, who had worked in core services, told the AP in November that engineering team clusters were down from about 15 people pre-Musk - not including team leaders, who were all laid off - to three or four before even more resignations.
Then more institutional knowledge that can't be replaced overnight walked out the door.
"Everything could break," the programmer said.
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