SINGAPORE (BLOOMBERG) - Gold's on a roll, courtesy of the Federal Reserve.

The precious metal is heading for the biggest weekly advance since July after US central bankers opted once again to leave interest rates unchanged while reining in their outlook for future increases.

Bullion for immediate delivery traded little changed at US$1,336.95 (S$1,808) an ounce at 8.53am in Singapore on Friday (Sept 23) after capping a fourth day of gains on Thursday, according to Bloomberg generic pricing.

The metal has climbed 2 per cent this week, the most since the period to July 29, as the dollar fell and investors boosted holdings in bullion-backed exchange-traded funds.

Gold is headed for a third quarterly gain in what would be the longest rally since 2011, when prices rose to a record.

On Wednesday, the Fed scaled back tightening plans and the Bank of Japan tweaked its stimulus focus, fueling bets European policy makers will keep their easing stance. Efforts by the world's top central banks to bolster growth including low or negative rates and asset purchases are driving demand for bullion as a store of value.

"The inaction by the Fed revived investor appetite for gold," Australia & New Zealand Banking Group Ltd. wrote in a note. "While a cut in the Fed's outlook for rates and the weaker US dollar no doubt played a part, the continued efforts by Bank of Japan to bolster economic stimulus also helped."