The San Francisco-based company acknowledged the problem, saying in a statement that its engineers were “currently working to resolve the issue,” although it didn’t go into further detail. It is the second time in just over a month that the site has been hit by problems.

Visitors to the site on Thursday were greeted with a half-formed message saying that “Twitter is currently down.” The fields where a reason for the outage and a deadline for restoring service were apparently meant to go were filled with computer code.

Sluggishness or outages were reported for more than an hour in countries in the Americas, Europe, Asia, and Africa.

Some users were able to post updates — known as “tweets” — through their phones or third-party applications. Tweets about the Olympic torch, which is wending its way through central London, still poured in, albeit far more slowly than earlier in the day.

Service appeared to be coming back to normal later Thursday, to the relief of many self-proclaimed “Twitter refugees” who’d flooded Facebook with complaints about the outage.

The Olympics are expected to bring an unprecedented surge of activity by sports fans on social networking sites such as Twitter. At the recent European Championship final, users fired off more than 15,000 tweets per second, setting a sports-related record for the site.

Social media users were already complaining about an earlier outage that affected Google’s chatting services. The Mountain View, California-based company said Thursday morning that the majority of users were seeing error messages and unable to use its Google Talk service. The issues were resolved five hours later.

In June, Twitter experienced an outage that lasted about two hours, which the company blamed on a technical glitch.