Millions of O2 customers have been left without coverage after their network went down.

The operator say 31 million mobile users have been affected by the outage, which began around 6am this morning.

The company tweeted at 7:30am after customers reported being unable to access the internet and other services due to a fault with the company network which impacted mobile data. 

The company said that the problem stemmed from a global software issue with third-party supplier Ericsson, which has also affected other mobile operators around the world.

More than 25 million O2 customers have been hit by the problem which affects several other mobile networks, including Sky, Tesco and Giffgaff, bringing the total affected to 31 million. 

O2 said fixing the issue remains a "top priority" but admitted that they do not know when the service outage will end. 

A spokesperson for O2 said: "The network issue we are currently experiencing remains a top priority for us and we are working as quickly as possible to fix the issue.

"All O2 technical teams are working closely with one of our third party suppliers who has identified a global software issue in their system which has impacted data services.

"As a result of this incident, we are experiencing a high demand on our network which means some customers may have issues making and receiving voice calls.

"We believe other mobile operators around the world are also affected.

"We apologise to our customers for any inconvenience."