UK customers have reported not being able to use mobile data to access the internet and other services on the company’s network.
It has confirmed engineers are working to fix the issue.
“We are aware our customers are unable to use data this morning,” the company said on its official Twitter account.
“Our technical teams are working on the issue with high priority. We are really sorry and working as hard and as fast as we can to fix this.”
The service status page of the O2 website added that “voice calls are working OK” and apologised for any inconvenience caused.
Other mobile networks, including Sky, Tesco and Giffgaff have also been affected by the problem because their networks use O2 services. O2 said it would share further updates as soon as they were available.
Says Ernest Doku, mobiles expert at uSwitch.com:
“O2 users affected by this mobile data outage will understandably be concerned and frustrated. Customers who are suffering can keep a track of this incident using O2’s own network status checker and ask the provider to keep them posted.
“In the meantime, O2 customers can still place and receive calls, but will have to resort to using WiFi if they want to get online.
“For the millions of users who are out and about and rely on smartphone maps to get around, it’s worth considering that apps like Google Maps allow customers to download maps on WiFi and view them offline.
“With little idea of when this problem will be sorted, it’s worth preparing before heading out to make sure you’re not caught out by this data downtime.”