With growth still sluggish in the $1.3 trillion mortgage market, NAB and ANZ are jostling to expand market share after ANZ last month cut its mortgage rate by more than the official move.

Commonwealth Bank has also recently increased its growth rate, putting the spotlight on Westpac, which has the highest standard variable mortgage rate among the big four and has been gradually losing share to its rivals.

Although its pricing strategy has bolstered profits so far, some believe Westpac's relatively high prices are holding back its growth prospects, and it may need to cut rates to win new business.

Nomura analyst Victor German referred to official figures that show Westpac's mortgage book grew by an annual rate of 3.3 per cent a year in the three months to April, compared with industry-wide growth of 5.7 per cent.

Over the same period, NAB's mortgage book grew at an annual pace of 7 per cent, ANZ's grew by 6.8 per cent and CBA's by 5.9 per cent, he said.

Westpac's standard variable rate of 6.26 per cent is 13 basis points higher than rates offered by ANZ and NAB. ''ANZ and NAB continue to gain market share and CBA appears to be closing the gap,'' Mr German wrote in a note to clients. ''We expect [Westpac] to ultimately use price to arrest market share losses.''

The prediction comes before the Reserve Bank's Tuesday board meeting, which markets are betting will result in the cash rate being left unchanged at 2.75 per cent.

Macquarie analyst Mike Wiblin has also argued Westpac may need to move from ''harvesting'' profits to ''growth mode,'' which would put pressure on margins.

After reporting a cash profit of $3.525 billion in the latest half, Westpac chief executive Gail Kelly said the bank would look to lift its mortgage growth across its stable of brands, which include St George, Bank of Melbourne, RAMS and BankSA.