A wave of unauthorised transactions has hit a major Philippine bank, triggering fears of hacking even as company officials said Wednesday it was an internal computer error.

Customers of Bank of the Philippine Islands (BPI) woke up Wednesday unable to access their accounts online with many shocked to see unauthorised withdrawals and deposits.

BPI said in a statement the problem was caused by an ‘internal data processing error’ that had been identified.

Efforts to fix the problem were ‘progressing well’ and the glitch was expected to be resolved within the day, the bank added in a new statement.

Online transactions remained suspended but bank branches were open, although transactions took much longer.

‘We wish to assure all clients that the integrity of their transactions and account balances will be maintained,’ it said.

Nestor Espenilla, the incoming governor of the Bangko Sentral ng Pilipinas, the country's central bank, said they had accepted ‘for now’ BPI's explanation that no hacking was involved, but would still conduct its own probe.

‘We have no reason to believe otherwise at this point of time, but as I said this is standard operating procedure, we always verify every incident that we are aware of,’ Espenilla said in a radio interview.

‘For now I think it's important that BPI resolves it as quickly as possible. We take their assurance that this is not a hack and no money will be lost.’

The bank said the error had led to some transactions between April 27 and May 2 to be ‘double posted’ starting on Tuesday.

Customers vented their frustrations through social media.

‘I had 3 unauthorize atm withdrawals! What the heck! I don't have any money left on my Personal acct!!’ a customer named Belle tweeted.

‘They didn't only take my savings, I am now in debt,’ read a Tagalog post by iamEm-em on a BPI Twitter page.

A user called wild flower wrote: ‘I lost my money... I only have 15 pesos (30 US cents) left on my pocket. How can I go home? Fix it please.’

The world has been on edge about hacking incidents following the world's biggest ransomware attack last month that struck hundreds of thousands of computers worldwide.