(UPDATE) Bangko Sentral ng Pilipinas Governor Benjamin Diokno said he was in touch with BDO Unibank and Unionbank over reports on social media that some accounts were hacked.
He added that affected customers would be reimbursed.
Clients of Sy-led BDO, the country's largest bank, have aired their complaints on Facebook about their accounts getting hacked with thousands of pesos transferred to a Unionbank account.
The Manila Bulletin reported that the money stolen from BDO accounts was used to buy bitcoin via Unionbank.
Diokno said the central bank had been monitoring a "surge" in complaints since the week of December 6.
"We are in close coordination with BDO as well as UBP (Unionbank of the Philippines) on this incident to ensure that remedial measures are being undertaken including reimbursement of affected consumers," he said.
"Rest assured that we continue to collaborate and engage stakeholders to ensure the safety and integrity of the financial system as well as the protection of financial consumers," he said.
The hacking complaints followed weeks of a surge in spam text messages offering jobs and discounts, prompting warnings from carriers Globe and Smart to customers to be wary of "smishing" or SMS phising scams that are designed to steal personal data.
In a statement posted on its website, BDO said it was aware of the "sophisticated fraud technique," adding that it had implemented additional security controls to block further attempts to hack its clients' accounts. It had also required its online banking users to update their passwords.
"We assure our affected innocent clients that we will reimburse their losses," it stated.
"Cybersecurity is a focal point of the banking sector. We at BDO are continuously investing and working towards improving our security infrastructure to protect our clients' money. While we have put back-end measures in place, we appreciate our clients' continued vigilance to combat fraud," it added.
On Saturday, December 11, BDO advised customers to change their online banking passwords to guard against scammers that pounce during Christmas, when workers receive their bonuses.
That post attracted comments from clients who said their accounts were hacked.