Microsoft traced the failure to a fault introduced during an earlier network capacity upgrade, and says a full post-incident report is coming.
Services remain uneven, and the disruption reached hospitals and airports in Britain, exposing how much public infrastructure depends on one cloud vendor.
Patients and members of the public may face delays until service is fully restored, and the incident has renewed debate over reliance on a few large providers.
Recovery is gradual as servers return to service, and Microsoft has not said when full service will be restored.