Japanese operator KDDI apologised after a network failure caused customers across the country to struggle with voice and data services, reporting the problems had been largely resolved after two days.

KDDI reported a facility failure in the early hours of 2 July had caused congestion in its VoLTE switchboard.

In a series of updates to customers, KDDI noted it had restored data connectivity in Western Japan at 11am local time on 3 July, with Eastern Japan switched-on six hours later.

By 3pm today (4 July) KDDI stated users could still find voice calls difficult due to “flow control” being undertaken while it was conducting further network tests, but two hours later it reported full services had “almost recovered nationwide” and advised anyone still struggling to reset their devices.

The operator repeatedly apologised for the issues across its various social media channels during the outage.

In addition to communications services, Nikkei Asia reported the incident caused major issues in the country including to weather data transmissions, connected car applications and parcel deliveries.

Nikkei Asia also highlighted the issue had drawn the ire of politicians, with Japan’s deputy Chief Cabinet Secretary Seiji Kihara demanding KDDI provide a detailed explanation, and Communications Minister Yasushi Kaneko stating he believed it should be classified a “serious incident”.

The scale of the outage has not been fully reported by KDDI, but Reuters estimated almost 40 million users had been impacted.