Westpac is the first major bank to increase interest rates on its fixed rate home loans and investment loans, but market watchers expect others to follow.

Property investors who take a Westpac five-year fixed rate mortgage from next week will see an increase of 0.6 percentage points to 4.59 per cent in the interest rate - the biggest of the increases.

Those who already have a Westpac fixed rate loan will be unaffected.

Figures provided by comparison site Canstar show property investors taking a Westpac five-year mortgage from next week who borrow $450,000 will pay an extra $158 dollars a month in repayments over 30 years.