SYDNEY - [AAP] National Australia Bank (ASX: NAB) has fired several bankers and reprimanded dozens more after discovering about 2,300 mortgages may have been issued without proper documentation.

NAB on Thursday said a review found about 2,300 mortgages since 2013 may have been submitted without accurate documentation, with many cases involving overseas borrowers.

Twenty staff in NSW and Victoria have had their employments terminated, or are no longer employed by the bank, and another 32 have faced consequences including pay cuts.

"What occurred was unacceptable," NAB consumer bank chief Andrew Hagger said.

"We have investigated this matter thoroughly, and, as we have always said, whenever we find issues we will investigate them, fix them, and hold people to account--and we did."

NAB said it became aware of the matter in October 2015 and had been in regular contact with the Australian Securities and Investments Commission since informing the regulator in December the same year.

NAB has started contacting the affected customers and asking them to take part in a loan review, which may include verification of documents submitted in their initial application.

Compensation will be offered as appropriate, the bank said.

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