The US has reported its first case of Omicron and South Africa's daily COVID-19 case numbers have virtually doubled each day this week, according to its health department.

The World Health Organisation said the COVID-19 pandemic was "the health crisis of our time" and said at least 23 countries from five of six WHO regions had now reported cases of Omicron and it expected that number to grow.

The S&P 500 closed down 1.18% in its worst two-day selloff since October 2020, Bloomberg reported.

Base metals were mostly higher on the London Metal Exchange, although cash copper was down 0.25% to US$9,492 per tonne.

Copper is worth $4.35 per pound on the spot market and Reuters reported Chile's state copper commission Cochilco slightly raised its copper price for this year to $4.23/lb, supported by a rally in the metal this year.

It had forecast a price of $4.20 for 2021 in September, and maintained its projection for $3.95/lb in 2022, the wire service said.

Copper producer Freeport-McMoRan closed down 2.29% and gold major Newmont lost 1.88% in New York.

The gold price is similar to yesterday, at $1,780 an ounce on the spot market.