* Focus turns to RBA's updated economic forecasts on Friday

* Origin Energy tops ASX200 losses on forecast cut

* AGL Energy slumps 3.6% on flagging impairment charge

* NZ50 closes at two-week low

Feb 4 (Reuters) - Australian shares snapped a three-day winning streak to close lower on Thursday, as healthcare and gold stocks declined, while power retailer Origin Energy was the biggest loser on the index after slashing outlook for its energy markets division.

The S&P/ASX 200 index ended 0.9% lower at 6,765.5.

Investors' focus shifts to comments from the Reserve Bank of Australia (RBA), slated to provide updated economic forecasts on Friday, after announcing earlier this week it would expand its bond-buying programme by another A$100 billion.

Electricty retailer Origin Energy dropped 6.9% to a three-month low after downgrading the fiscal 2021 outlook for its energy markets division.

The country's top power producer AGL Energy slumped 3.6% after saying it expected to book a A$2.69 billion charge in its half-year results to write down the value of its assets and previously signed wind energy contracts.

Miners lost 0.5%, with world's largest miner BHP falling 0.5%.

Gold stocks slid 2.8% to hit their lowest in nine months after bullion prices eased overnight. Newcrest Mining shed 2.2% and Ramelius Resources plunged to a near-nine-month low.

Healthcare stocks also declined, with sector heavyweight CSL shedding 1.8%.

New Zealand's benchmark S&P/NZX 50 index ended 0.8% lower at 12,992.14, with eight out of nine sectors closing in the red.

Telecom services provider Chorus Ltd fell 3.8% to be the top loser on the benchmark. (Reporting by Harish Sridharan in Bengaluru; editing by Uttaresh.V)