Mizuho Bank suffered its fifth system failure of the year on Friday that prevented the completion of deposits, withdrawals, transfers and other transactions at its branch counters across Japan, its parent company said.

Mizuho Trust & Banking Co. also suffered similar malfunctions at its branch counters, according to major banking group Mizuho Financial Group Inc., but the group's internet banking and automatic teller machines were unaffected.

An outlet of Mizuho Bank is pictured on Aug. 20, 2021, in Tokyo's Shimbashi area. (Kyodo)

The group said its fifth system failure since February was caused by a problem in a server connecting Mizuho's core accounting system and terminals used at its branch counters and that switching to a backup device also failed for some reason. The system was fixed at around noon.

The banking group learned of the problem on Thursday, but it was unable to restore the system in time for the start of transactions at the counters on Friday morning. Its customers were informed by a notice on the group's websites posted 30 minutes before branches opened.

"We take it extremely seriously that the failure happened while we were working to prevent any recurrence following the previous crashes in February and March," Mizuho Financial Group President and Group CEO Tatsufumi Sakai said at a press conference as he apologized to those affected by the problem.

Asked about the possibility of his resignation, Sakai said he wanted to fulfill his responsibility by looking further into the cause of the latest failure and beefing up the preventive measures the company is currently implementing.

All of Mizuho Bank's 463 branches and Mizuho Trust & Banking's 60 branches were affected, but the number of transactions disrupted by the failure has yet to be tallied, according to the banking group.

Chief Cabinet Secretary Katsunobu Kato told a press conference earlier in the day the system failure "significantly damages the credibility of financial institutions and is very regrettable," noting that the bank experienced four separate problems in February and March that "greatly affected individual and corporate users."

Mizuho Financial Group Inc. CEO Tatsufumi Sakai (L) and Mizuho Bank President Koji Fujiwara bow in apology at a press conference in Tokyo on Aug. 20, 2021. (Kyodo)

The four earlier system failures occurred over about two weeks from Feb. 28 this year. A total of 4,300, or about 80 percent, of Mizuho's ATMs nationwide were affected, with more than 5,000 bank cards and bank books swallowed up by the machines.

The latest crash came as the Financial Services Agency is investigating the system failures in February and March with an eye to issuing a business improvement order to Mizuho.

A third-party panel consisting of lawyers and system management experts said in a report released in June that the previous four problems were caused by factors such as inadequate deployment of technology-related staff and a corporate culture in which employees hesitated to speak up during emergency situations to avoid responsibility.

Mizuho users around the country expressed disappointment over the system failures.

"With problems like this occurring repeatedly, it makes me want to change the bank I use," said a man in his 60s who had visited a branch of the bank in Osaka to pay tax. He learned about the failure only after he visited the branch in the morning.

A woman in her 30s who used an ATM in Tokyo expressed her frustration with the latest system failure. "I thought not again," she said.

The financial group also suffered large-scale system failures in April 2002 and March 2011.

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