UPDATE: Google has published a statement on its Gmail dashboard - "The problem with Gmail should be resolved. We apologize for the inconvenience and thank you for your patience and continued support."
"System reliability is a top priority at Google. We are making continuous improvements to make our systems better.."
Customers are reporting outages in Gmail and several other Google services across the world.
The outage began around 05:00 BST on Thursday, according to tracking site DownDetector, which showed continuing high numbers of complaints in the UK and multiple other countries for a number of Google services.
Thousands of complaints were registered on the site, with many users unable to sign in as they logged in to start the working day.
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Google has acknowledged the service disruption and said that it was investigating the issue.
According its Gmail service dashboard, a response is expected soon - although the company has been promising a response to users within the next few hours for most of the morning so far.
Along with Gmail, users also reported issues with Google Drive, with many unable to login to Gmail, make searches, or upload or access content from their Google Drive account.
Others issues noted by Google included Meet recording issues, CSV user upload issues in Admin Console, and posting message issues in Google Chat. Newly reported issues include Sites adding new pages issues, Keep issues, and Voice mail issues - making this a significant outage for Google.
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