Aug 10 (Reuters) - Australian shares slipped on Monday as losses in lender Westpac after its quarterly update weighed on financials, offsetting gains in miners ahead of the Reserve Bank of Australia's policy decision.

The S&P/ASX 200 index was down 0.5% at 9,220.30 points, as of 0057 GMT. The benchmark gained 3.2% last week.

Risk sentiment roughened in a closely watched fiscal 2027 earnings season, with shares of Westpac sliding more than 5%, their biggest intraday drop since March 30.

The Australian lender forecast investor housing credit growth would halve next year and reported a 20% fall in mortgage applications. It reported cash earnings of A$1.8 billion for the quarter ended June 30, down from A$1.9 billion a year earlier.

Westpac's decline dragged the financials sub-index down 1.9%, with shares of Commonwealth Bank of Australia ( CBAUF ), ANZ and National Australia Bank ( NAUBF ) falling between 1.3% and 2.4%. The sub-index posted its largest intraday loss in three months.

Investor focus will also shift to the RBA's decision, due on Tuesday, with markets widely expecting the central bank to keep interest rates unchanged while looking for clues on the monetary policy outlook.

Countering losses, miners jumped 1.4%, lifted by strong metal prices. [MET/L] [IRONORE/]

Mining giants BHP Group and Rio Tinto gained above 1% each, while peer Fortescue added 0.7%.

The gold sub-index followed suit and rose more than 3% to its highest level since mid-April, tracking gains in bullion prices. [GOL/]

Shares of gold miners Evolution Mining and St Barbara added 1.3% and 4.7%, respectively.

In company news, shares of Treasury Wine Estates rose nearly 8% after the Penfolds winemaker said it will reduce the size of its U.S. North Coast vintages from 2026, and write down inventory, mainly bulk wine.

It also forecast its FY26 unaudited earnings before interest, tax, SGARA and material items (EBITS) at A$492.3 million, topping the prior outlook range of A$480 million to A$490 million.

New Zealand's benchmark S&P/NZX 50 index rose 0.5% to 13,892.88 points.