TORONTO -- Rogers wireless services were starting to return to normal Monday evening, the company said in a tweet, after a countrywide cellular service outage left many Rogers and Fido wireless customers unable to make calls, send text messages or use mobile data.

The company has also identified the root cause of the intermittent outage and was still working to restore full service to its customers.

A recent Ericsson software update affected a piece of equipment in the central part of the company’s wireless network, which led to intermittent congestion impacting many customers across Canada, Rogers Chief Technology Officer Jorge Fernandes said in a statement posted on the company’s website.

“We have addressed the software issue and our engineering and technical teams will continue to work around the clock with the Ericsson team to restore full services for our customers,” Fernandes said, adding that the company did not know when service would be restored “as it may take us several hours to get everything back up and running normally.”

DownDetector.ca, a website that tracks network outages, says it started to receive reports of outages just after midnight eastern time on Monday, before peaking at more than 12,000 reports by 8:30 a.m. The website show reports of outages in every province, though most reports have largely clustered around Southern Ontario, the Greater Montreal Area and Calgary.

Rogers and Fido customers impacted by the cell outage can still make 911 calls. However, police departments across Canada, from Winnipeg to Peel Region, Ont., are warning those who need to make an emergency call to stay on the line, as 911 operators will not be able to call back if the call becomes disconnected.

School boards, such as the Durham Catholic District School Board and Dufferin-Peel Catholic District School Board in Ontario, had also said school-issued iPads and hotspot devices will not be able to connect.

A spokesperson from Rogers said in an email statement earlier on Monday that the company ​was working to restore services and that business and residential wireline internet services were not affected, but did not answer questions on how many customers were affected.

"We sincerely apologize and thank our customers for their patience," the spokesperson said.

With files from Solarina Ho