US President-elect Joe Biden has warned Americans of a “very dark winter” ahead and implored them to wear masks as the country tops 10 million virus cases.

The grim milestone came just 10 days after coronavirus infections across the US topped nine million.

In his first public remarks since his victory speech on Saturday, Mr Biden announced a task force to respond to the pandemic. He also said masks were the most effective tool against the virus until a vaccine was delivered.

“It doesn’t matter who you voted for, where you stood before Election Day. It doesn’t matter your party, your point of view, we can save tens of thousands of lives if everyone would just wear a mask for the next few months. Not Democrat or Republican lives, American lives,” he said in Delaware on Monday (local time).

“Please, I implore you, wear a mask. A mask is not a political statement, but it is a way to start pulling the country together.”

Masks have indeed become a political statement in the US, with President Donald Trump and many senior Republicans and presidential advisers often refusing to wear one. Last week, White House chief of staff Mark Meadows – who frequently refused to wear a mask – was confirmed to have caught the virus.

“The goal of mask-wearing is not to make you less comfortable, or take something away from you. It’s to give something back to all of us, a normal life,” Mr Biden said.

“The goal is to get back to normal as fast as possible. Masks are critical in doing that. It won’t be forever, but that’s how we’ll get our nation back.”

Tweet from @JoeBiden

Mr Biden routinely slammed Mr Trump for his handling of the crisis, while the President falsely claimed the US was “rounding the turn” despite evidence of a third wave raging across the nation.

By late Monday (local time), the pandemic had killed nearly 240,000 people in the US.

Hospitalisations and infection rates are also rising – with more than 100,000 new daily cases reported on average in the past week. Caseloads have been on the rise since September.

The record for daily infections was on Saturday, with more than 128,000.

Fatalities topped 1000 on several days last week.

The surge is widespread across the US and particularly severe in Minnesota, Illinois and other northern states.

In New York City, which gained control of its infection rate after being the national epicentre of the outbreak in the spring, Mayor Bill de Blasio urged residents to prevent a “dangerously close” second wave and potential ensuing lockdown measures.

“We have to do everything in our power to stop coronavirus from reasserting in New York City,” he said, calling on people to wear face masks and maintain social distancing.

Health experts are worried that with colder weather and people spending more time indoors, the virus will spread more rapidly, and authorities are cracking down with new mitigation efforts.

In a milestone in the search for a defence against the outbreak, US pharma giant Pfizer and German firm BioNTech have announced their experimental vaccine is 90 per cent effective in preventing COVID-19.

More than 50.7 million coronavirus cases have been recorded worldwide and over 1.2 million people have died, according to Johns Hopkins University.

After the US, India and Brazil have the highest number of confirmed infections, at 8.5 million and 5.6 million, respectively.

-with AAP