KDDI said in a statement at 9:00 a.m. Monday (0000 GMT) that data transmission had largely been restored but users may experience difficulty making voice calls due to the restrictions.
The disruption, which began in the early hours of Saturday morning, was caused by an equipment malfunction and affected services ranging from weather data to parcel delivery and banking.
“The main risk is that more outages are possible because the complexity of the network is difficult to manage,” said Kirk Boodry, an analyst at Redex Research, which publishes on the Smartkarma platform.
Shares of KDDI, which were down 1.5% at 10:03 a.m., are up 26% year-to-date.