The banks are the first two of the Big Four lenders dominating Australia's banking system to implement the loosening of mortgage lending rules, introduced by the prudential regulator earlier this week.

From Tuesday, Westpac now assesses the serviceability capacity of its customers using the lower of 2.5% over its lending rate, or a minimum 5.75% floor test, according to its website.

That compares with a 7.25% minimum testing rate the banks used before the regulator removed the mandated floor.

The Australian Prudential Regulation Authority (APRA) earlier this month scrapped the minimum testing rate as it added to the stimulatory tools being deployed to revive the country's sluggish economy.

ANZ told clients on Friday that its new floor rate for retail lending would fall to 5.50% from Monday, according to a marketing memo seen by Reuters.

A spokeswoman for Commonwealth Bank of Australia said the bank was in the process of reviewing its own testing rate, while representatives from National Australia Bank  did not return an emailed request for comment.

Following a protracted property downturn, the Reserve Bank of Australia (RBA) on Tuesday said house prices were now stabilising and APRA's credit easing measure was "likely to see a boost in borrowing capacity for many new borrowers", its July policy meeting minutes showed.

The central bank, however, said it does not expect a material pick-up in borrowing.

The move means that borrowers applying for home loans carrying variable loan rates of about 3.5% will now be tested on their ability to repay a loan carrying 6% interest - that is 1.5 percentage points lower than before.

According to analysts, every 1% drop lets home buyers borrow up to 10% more.

The spring season in the housing market would be a key litmus test for whether the changes have worked, Royal Bank of Canada said in a note to clients.