An error during routine maintenance on Facebook's network of data centres caused Monday's collapse of its global system for more than six hours, leading to a torrent of problems that delayed the repairs, the company said on Tuesday.

The outage was the largest that Downdetector, a web monitoring firm, said it had ever seen. It blocked access to apps for billions of users of Facebook, Instagram and WhatsApp, further intensifying weeks of scrutiny for the nearly US$1 trillion company.

At a US Senate hearing on Tuesday...