Microsoft Outlook is down leaving users unable to access their emails.
Thousands attempting to log-in to their email accounts have been met with a “service unavailable” error message.
The Outlook.com platform began reporting issues on Thursday morning and Microsoft has confirmed it is investigating the cause.
A message on the company’s service status website said the fault has left users unable to access emails, and it is “collecting additional data from the affected infrastructure to aid in our investigation to determine the cause of impact”.
In a further response to users on Twitter, Microsoft apologised and said its engineering team is “aware and is actively investigating” the problem.
The popular email platform supports Outlook, Hotmail and Windows Live email accounts and is estimated to have more than 400 million users, although the number of those affected by the outage has not been confirmed.
Many users have taken to social media to express their frustration at the incident - which has left people unable to access their work emails at a time when large numbers are working from home and rely on emails to communicate with colleagues.
According to web service monitoring platform DownDetector, users across Europe, as well as parts of Africa and India, have reported problems with Outlook.
One user shared: "I have tried to login in this morning to my emails but cant and wont load at all just says... Error. service unavailable."
Another posted: "Can't open my outlook app on android phone, can access through chrome but app just shuts down before home loads."
The site said issues with Outlook were first reported at around 7am on Thursday morning and since then more than 3,000 reports from users struggling to access the platform have been made to DownDetector.
