Customers of the mobile network, Three, have told the BBC they cannot make 999 calls, as the network faces a significant outage.

The firm has apologised after more than ten thousand people told outage tracker Downdetector they were unable to make or receive phone calls on Thursday.

Three told the BBC in a statement earlier on Thursday its customers were still able to make 999 calls.

However, the BBC has been told by members of the public that 999 calls will not connect from their devices using the Three network. The BBC has not been able to independently verify their claims.

The BBC has approached Three for comment.

“We’re aware of an issue affecting a small percentage of voice services, our team are working hard to fix this as soon as possible,” the firm previously told the BBC.

“We’re really sorry for any inconvenience caused.”

The firm said people were still able to use mobile data services and make 999 calls during the outage, though multiple people have told the BBC that is not the case.

There have also been several thousand reports from users of Smarty and ID Mobile – smaller mobile companies which use Three’s network.

Three’s support team has been telling customers that it does not “have a timeframe” for a fix, but that the firm is “working hard to resolve this as soon as possible”.

Three has around 10.5m customers across the UK, according to its website, but it is unclear how many of them are affected by the outages.

Many people on social media have shared their frustration at the outage and described the disruption they said it had caused them.

One person claimed they had “missed a medical appointment” as a result of being unable to receive calls, while another said the issues had left their daughter “stranded”.

And several people have claimed they would be leaving the network altogether.

In a statement the regulator Ofcom said: “We are aware that Three is experiencing problems with its network. We are in contact with Three to establish the scale and cause of the problem as soon as possible.”

It is not known whether customers will be able to claim compensation for the outage, although according to the Ofcom website it “may be appropriate” for providers to offer refunds “while repairs are being made”.

It comes a month after the UK regulator gave the go-ahead for Three to merge with former rival Vodafone in a £16.5bn deal.

It comes the same day a major outage affected artificial intelligence tool ChatGPT.