By Makiko Yamazaki and Yuki Nitta
TOKYO (Reuters) -Mizuho Financial Group's main banking unit suffered a system glitch that left branches nationwide unable to process transactions on Friday, the latest in a series of embarrassing system errors at Japan's No. 3 lender.
The glitch in Mizuho's core "Minori" banking system prevented in-person transactions on Friday morning, with service at about 460 branches mostly restored by 09:45 a.m. (0045 GMT) local time.
Mizuho shares closed down 1%, in line with the benchmark index.
The outage is the latest blow to the reputation of Mizuho, which suffered a series of breakdowns between February and March this year despite a $3.6 billion overhaul of its systems in 2019.
That revamp followed two large-scale breakdowns in 2002 and 2011.
The fresh outage piles further pressure on group CEO Tatsufumi Sakai and banking unit head Koji Fujiwara, who both took temporary pay cuts following the earlier tech trouble.
"As this is the fifth glitch in a short period of time, we take this extremely seriously," Sakai told a press briefing.
Asked about his responsibility, Sakai said he wants to fulfil his responsibility by beefing up prevention measures which the bank has been pursuing since the previous glitches.
The glitch also affected the group's trust bank unit, while automated teller machines (ATMs) and online banking services were unaffected.
Mizuho first detected the glitch on Thursday evening, but said its backup system failed to operate immediately.
In-branch services are widely used by Mizuho's older and corporate customers.
"This latest trouble has pushed me towards thinking about closing my account," Yoshiyuki Sakata, 41, a Mizuho customer in Chiba Prefecture, near Tokyo, told Reuters.
Japanese chief cabinet secretary Katsunobu Kato told a regular news conference that the system glitch was regrettable and that regulators must respond firmly.
"We want Mizuho to restore its system and respond carefully," Finance Minister Taro Aso told reporters. "We have not received any report from Mizuho yet as to how they are dealing with it."
Mizuho shares have gained 18.6% this year outperforming the Nikkei 225, which is down 1.6%.
A report https://www.reuters.com/world/asia-pacific/mizuhos-system-failures-caused-by-corporate-culture-third-party-probe-says-2021-06-15 in June commissioned by Mizuho found that its corporate culture - including an atmosphere where managers are reluctant to express their opinions and unable to respond well to crises - was to blame for its tech problems.