T-Mobile and other major US wireless carriers and telecom providers appeared to be inundated with reports of outages affecting thousands of customers, according to service tracking site Down Detector.

“After our teams got things working last night, we recommend a quick device restart (power it all the way off and back on) to make sure you have a fresh network connection,” T-Mobile tweeted.

Problems started Monday aftrenoon.

“Our engineers are working to resolve a voice and data issue that has been affecting customers around the country,” tweeted Neville Ray, T-Mobile’s president of technology on Monday afternoon.

Ray added that T-Mobile engineers hope to fix the “voice and data issue” soon. At 6 p.m., Ray tweeted that data services were back up, but that calls and texts were still having problems. He recommended customers use WhatsApp, iMessage and other communications tools instead.

The scope of the outage wasn’t clear, but Ray said it has affected customers around the country. T-Mobile representatives did not reply to further questions.

Down Detector tracked outages and service problems across numerous carriers.

A check of the website’s reports early Tuesday revelaed that most carriers were returning to more normal levels of service although Cox, Comcast and Century Link had problems around 2 a.m.

People on Twitter complained that calls were not going through. The Redmond, Washington, police department tweeted that T-Mobile customers should have “an alternate plan in place in the event you need to call 911.”

AT&T and Verizon both said their networks were operating normally. But calls between their customers and T-Mobile customers could have problems because of T-Mobile’s issues.

T-Mobile became one of the country’s largest carriers, along with AT&T and Verizon, after buying rival Sprint. The company has started integrating the two networks.

The Federal Communications Commission, which oversees voice and data networks, said its public-safety bureau is looking into the problem.

T-Mobile paid a $17.5 million fine for two nationwide service outages on the same day in August 2014, which together lasted three hours and prevented customers from being able to call 911.