(Bloomberg) -- Japan’s second-largest mobile carrier by subscribers fell the most since March after a nationwide disruption of its services over the weekend. As many as 39 million mobile lines were affected, preventing users from making calls or using data services, until the network was largely restored early on Monday.

KDDI Corp. dropped as much as 3.9%, an unusually large swing for a typically stable stock. Shares slightly recovered since, but still trailed the overall market, with the Topix index up 1.4% as of 9:41 a.m. in Tokyo.

The network disruption began early Saturday and impacted KDDI users nationwide as well as other platforms using the carrier’s network, such as weather services, parcel deliveries and ATMs. Rakuten Mobile, operated by e-commerce company Rakuten Group Inc., said its users were also affected. KDDI said Monday there were still some lingering issues with calls and the company can’t for now estimate when service will be fully restored.

“We deeply regret what happened, as a telecommunications company that should provide a stable service and support social infrastructure,” KDDI President Makoto Takahashi said at a news briefing Sunday, according to local broadcaster NHK. “We’re doing our best on recovery efforts.” 

This isn’t the first time Japan has suffered significant mobile network problems. NTT Docomo Inc. reported an outage in October that disrupted phone and data communications services nationwide. The government told NTT Docomo in November to improve operations following the incident. 

The incident is “very regrettable,” Yasushi Kaneko, minister in charge of Japan’s communications, said at a press conference Sunday. KDDI should take drastic measures to prevent any recurrence, he said.

“This will have a negative impact on share prices in the short term,” Mitsubishi UFJ Morgan Stanley analyst Hideaki Tanaka wrote in a report after the KDDI disruption. “But this is a risk that all major carriers have. I don’t think this will cause major changes to the number of subscribers.”

(Adds comment from KDDI in third paragraph.)

©2022 Bloomberg L.P.