Mizuho Financial Group Inc., Japan's third-largest bank by assets, is experiencing computer problems that are affecting its automated teller machine network as consumers are frequently withdrawing cash in the aftermath of last week's earthquake, tsunami and subsequent nuclear power plant problems, according to various reports.

Computer issues are also affecting Mizuho's online banking service and funds-transfer system. Tellers at all 440 Mizuho branches were unable to conduct cash transfers and money orders since March 15, according to The Wall Street Journal.

Mizuho said in a press release that as of March 16 it had been unable to complete 440,000 transactions valued at $7.2 billion. Some 1,600 ATMs and online banking services on March 17 stopped working for several hours before service was restored around noon local time.

Mizuho's president, Satoru Nishibori, told reporters during a press conference that a surge in financial transactions might be the cause of the computer problems. A bank representative told the Journal that Mizuho does not believe the earthquake caused the problems.

Another possible explanation for the problems could be recent system changes that enable ATMs to accept earthquake-relief donations, Nikkei reported. The news outlet also reported no other major financial institutions have reported any problems.