"We appreciate our customers' patience while we work to resolve this as soon as possible," the company said.
It comes as people on social media say they are struggling to access Vodafone customer service operators amid ongoing issues affecting mobile data and broadband.
Many have also said they are having difficulty accessing the company's website and app, which typically allow people to view the status of its network services.
Customers have also taken to social media to complain of "complete outages" in their area.
The issues appear to have begun for customers shortly after 15:00 BST.
Internet monitor Netblocks said in a post on X, external, live network data showed Vodafone was experiencing "a national outage" impacting both broadband and mobile data.
Some customers have expressed being doubly frustrated by not being able to access their Wi-Fi or mobile data.
"Sort it out soon please," wrote one frustrated X user - who said they were having to use a coffee shop's Wi-Fi to access online services without the means to do so using their mobile data or broadband.
Another said they were self-employed and could not work because of the outage, adding: "Never regretted more having my mobile and broadband on the same network."
The issues affecting Vodafone services are also impacting customers of other telecoms firms that use its network.
Downdetector saw a similar spike in reports on Monday afternoon from users of the mobile network Voxi, which is owned by Vodafone.
Lebara, which piggy-backs off Vodafone's network, has also been affected by the company's outage.