Tens of millions of cell phone users in Japan were unable to connect for most of the weekend in what is thought to be the country's worst ever service outage.

KDDI said the disruption began on Saturday and continued through Sunday, with some users still having problems on Monday.

About a third of the country's population was affected by the unprecedented outage.

Customers of UQmobile and Povo services, which use KDDI's infrastructure, were affected.

KDDI said it started when engineers were working on new equipment.

Users, some of them corporate customers, were unable to make calls or use the internet, leaving those desperate to make a call having to borrow a friend's phone.

Unable to make calls, do online banking, organize deliveries, book rides, and take advantage of the plethora of other services normally available to phone users, tens of millions of regular customers were left extremely frustrated

The incident made it hard for some services to respond to emergencies.

The president of KDDI apologized on Sunday and promised to respond according to Japanese law.

There is a recommended video.