A senior Reserve Bank official has taken a swipe at Australian banks for their lending standards, amid big errors in bank loan data that saw them understate the value of loans to investors by $50 billion.

RBA deputy governor Philip Lowe told a financial conference in Sydney that the central bank was concerned by reviews of loans to investors by the banks over the past six months that found "very large upward revisions to the value of investor loans outstanding".

Mr Lowe said more than 10 financial institutions, including two of the biggest lenders, found their outstanding investor loans were $50 billion, or 10 per cent more, than they previously thought.

"As lenders have looked more closely, what they have found has surprised and, to some extent, concerned us," he said.

The new figures mean that the total value of investor loans stands at more than $500 billion.

Mr Lowe said the new data showed that 40 per cent of all housing loans were taken out by investors, not the 35 per cent reported earlier in the year.

"While the reasons for some of these earlier errors have been identified," he said, "in other cases the reasons are unclear and lenders have not been able to provide comprehensive back data."

He said that the various data problems had reinforced the RBA's view that regulators had made the right call to crack down on investor loans.

Mr Lowe also told the conference that the RBA had also discovered that a sharp fall in bank lending to investors because a crackdown on investor loans by the banking regulator was not as dramatic as first thought.

He said some lenders had reported to the RBA that some loans that were recorded as investor loans were really owner-occupier loans.

"This is partly because, when faced with the higher interest rate on investor loans, some borrowers have indicated to their bank that they are not an investor, but rather an owner-occupier, and so should not have to pay the higher rate," Mr Lowe said.

"And it is disappointing that some lenders' internal systems have not been up to the task of reporting accurate data on the split between investor and owner-occupied housing loans."

Mr Lowe said further loan reclassifications were likely over coming months.

Late last year, the banking regulator, the Australian Prudential Regulation Authority, ordered banks to limit their investor lending to an annual growth rate of 10 per cent.