Property investors will bear the brunt of interest rate hikes from National Australia Bank and Westpac, as lenders fend off a squeeze on their profits from stiff competition and higher funding costs.

NAB on Monday said it would raise its standard variable rate for housing investors by 0.15 percentage points to 5.55 per cent, a move that will affect both new and existing customers.

Westpac, the country's second-biggest bank, will raise interest rates for all its customers with interest-only home loans by 0.08 percentage points.

Westpac's change will also affect new and existing loans, for both owner-occupiers and property investors, but will be mostly felt by investor customers, who tend to favour this type of loan because their interest costs are tax-deductible.