This means that the number of impacted customers is, in reality, likely to be much higher than 25 million.
The outage is also causing other disruptions, such as issues with public transportation. A complete and comprehensive root cause analysis is still in progress, Ericsson said. "Our focus is now on solving the immediate issues".
"The cause of today's network issue is in certain nodes in the core network resulting in network disturbances for a limited number of customers across the world, including in the United Kingdom", she said. "Ericsson sincerely apologises to customers for the inconvenience caused". Our technical teams are working with their teams to ensure this is fixed as quickly as possible.
"During the course of December 6, most of the affected customers' network services have been successfully restored", Ericsson explained.
O2's internet service has gone down this morning, leaving people with phones on the network unable to access the internet..
O2 chief executive Mark Evans said his teams were working hard with Ericsson to find a swift solution.
In Stockholm, Ericsson added it was taking "immediate action".
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"We're aware that our customers are unable to use data this morning", the company admitted in a statement. Work is now ongoing to fix the fault and customers are being encouraged to use wi-fi where possible.
Thousands of O2 customers have not been able to get online on Thursday morning following a technical fault with the network.
Other mobile networks, including Sky, Tesco and Giffgaff, were also affected by the problem because their networks use O2 services.
Computing will update this story as soon more news comes in.
The company said it would be closely monitoring data services over the coming days and promised to carry out a review to understand what went wrong.
As LTE networks become increasingly saturated, mobile network operators are planning for the 5G future.