MANILA (Updated) -- The Bangko Sentral ng Pilipinas (BSP) will conduct an investigation to determine how a number of Bank of the Philippine Islands (BPI) cardholders lost money in their accounts overnight.

"The BSP will also investigate and look into the matter and see what happened, what were the operational lapses that led to that so that we can also come up our own conclusion and see what action we need to take and also make sure measures are in place to prevent this from happening," said BSP Director Pia Roman-Tayag.

"For now, BPI assures us this is not a hack and problem will be fixed today (June 7) and no one will lose money," said BSP Deputy Governor Nestor Espenilla Jr. in a text message Wednesday, June 7.

"We'll investigate as soon as dust settles and customers are made whole," Espenilla added.

The glitch quickly spread in social networking sites on Wednesday, prompting bank clients to immediately check their accounts at nearby BPI branches and ATM machines.

Some reported not being able to access their BPI accounts on mobile, while others said there were unauthorized transactions that deducted money from their accounts.

But the BPI said in an advisory that the discrepancies reported in its clients' bank account balances was due to an "internal system error."

In its advisory posted on Facebook, the bank said the glitch caused some transactions occurring between April 27 and May 2 to be double-posted as of June 6.

It added that it has identified the root cause of the error and is temporarily suspending access to electronic channels to speed up rectification.

BPI assured its clients that it will resolve the matter within the day.

“We are pleased to report that our efforts to resolve an internal system error related to transaction mispostings are progressing well. All BPI branches are open and continue to service your needs,” the bank said.

It also assured its clients that "the integrity of their transactions and account balances will be maintained, and that none of them will lose money from this incident."

Espenilla, in an interview at ANC, said the central bank was not just concern about cyber security issues of the banks in the Philippines, but "we would like to make sure that our banks are taking proper measures to control all kinds of issues including operational errors."

He said those BPI customers who were able to receive additional funds in their accounts should not withdraw and spend the money.

"If a customer uses money that is not his own, that may rise to legal action," he said, adding the BPI incident was an isolated case.

For Roman-Tayag, it is premature for the BSP to discuss about a possible sanction, saying they have to do their investigation first.

"We don't want to focus our attention on that yet because our priority really now is for the records of the consumers to be fixed and we want the bank to focus their attention on that," she said.

"It depends, since the sanctions should be commensurate on what happened. We can't speak yet on what sanction to apply if they apply on what actually happened," she added.

She also advised consumers to always know their account balances, and if they notice anything out of the ordinary, "always keep your lines of communication open with your financial institution."

"If you are unable to get a response or unable to reach them, you can go to the Bangko Sentral ng Pilipinas. We have a financial consumer protection department where we can facilitate your conversations with your financial institution," she added.

She also cautioned the netizens to be careful in posting information in social media.

"Go straight to your financial institution of your bank if you have any questions rather than posting personal information online," she said.

With total assets of P1.45 billion as of end-2016, BPI is the third biggest universal bank in the country after BDO Unibank and Metropolitan Bank.

The bank has a network of over 800 branches in the Philippines, Hong Kong and Europe, and close to 3,000 ATMs and CDMs (cash deposit machines). (PNA/With Franz Correa/SDR/LMY/SunStar Philippines)