Vodafone customers across large parts of Europe are reporting being unable to use their mobile internet and broadband services.
Users in the UK, Ireland, Portugal, Germany, Greece and Italy took to social media - despite connectivity difficulties - to say there were problems.
There were also indications of disruption further afield - in Australia and India.
Vodafone in the UK said work was underway to solve the glitch but it was unable, at this stage, to give a definitive statement on the extent of the issue.
It is understood the company is re-routing internet traffic to get around the problem.
Problems were first reported before 3pm UK time, according to the outage reporting network Down Detector.
Vodafone Portugal told its customers via Twitter: "Hello, due to technical problems, we are experiencing difficulties in our fixed and mobile services at national level.
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"This situation is already in the resolution phase. We regret all inconvenience caused and thank you for understanding."
The glitch happened at a time when Vodafone is firmly focused on the launch of its first 5G services in the UK.
The 5G fanfare - slated for 3 July.- will be limited to seven cities initially.