Verizon Wireless has suffered a major outage across the US, with tens of thousands of users reporting that iPhones are stuck in 'SOS Mode.'

“We are aware of an issue impacting wireless voice and data services for some customers,” the company said in a statement.

“Our engineers are engaged and are working to identify and solve the issue quickly. We understand how important reliable connectivity is and apologize for the inconvenience.”

Issues began at around midday Eastern Time.

The Office of Unified Communications (OUC) in Washington D.C. said that the outage “may be affecting some users attempting to connect with 911.”

“If you have an emergency and cannot connect using your Verizon Wireless device, please connect using a device from another carrier, a landline, or go to a police district or fire station to report the emergency."

The cause of the outage is not yet known.