BEIJING, Dec 21 (Reuters) - Prices of most base metals were mixed on Wednesday as weak U.S. dollar and tight supplies offered some support, while the rapid spread of COVID-19 in top consumer China continued to fan demand worries.

Three-month copper on the London Metal Exchange was up 0.3% at $8,376 a tonne by 0837 GMT. The most-traded January copper contract on the Shanghai Futures Exchange advanced 0.9% to 65,760 yuan ($9,434.31) a tonne.

The dollar index, which measures the greenback against the yen and five other major currencies, was 0.04% higher at 104.02, having slipped 0.6% on Tuesday after Bank of Japan (BOJ) shocked the market by tweaking its bond yield control.

The index is heading for its biggest quarterly loss in nearly 12 years.

A weaker dollar makes the greenback-priced commodity more attractive to non-dollar buyers.

China's yuan eased against the dollar in thin trade, as sentiment remained depressed due to growing economic concerns from a spike in COVID-19 cases in the country.

Still, tight global stocks for metals including copper, aluminium and zinc, and news of possible production cuts lent some help.

Indonesia will ban exports of bauxite, the main source of aluminium, starting June 2023, President Joko Widodo said on Wednesday.

"We won't see much reaction from aluminium futures regarding the ban, because Indonesia's supply to China is not as significant as it used to be," a Shanghai-based futures trader said. "And the current focus of the market is macro-driven instead of production costs."

LME aluminium climbed 1.2% at $2,400 a tonne, zinc was down 0.9% to $3,055, lead slid 0.6% to $2,167.50, while nickel fell 1.2% at $28,005.

Bloomberg reported on Tuesday that Russia's Norisk Nickel , the biggest producer of refined nickel, is considering reducing output by 10% next year.

SHFE aluminium gained 0.5% at 18,655 yuan a tonne, zinc eased 0.1% to 23,480 yuan, nickel rose 1.8% to 217,780 yuan, and tin was up 1.6% to 194,650 yuan.

For the top stories in metals and other news, click or

DATA/EVENTS (GMT) ($1 = 6.9703 Chinese yuan renminbi) (Reporting by Siyi Liu and Dominique Patton; Editing by Rashmi Aich, Uttaresh.V, and Janane Venkatraman)