Photo taken in Arlington, Virginia, the United States, on Nov. 7, 2020, shows the live stream of Joe Biden delivering a speech in Wilmington, Delaware. (Xinhua/Liu Jie)

"We are still facing a dark winter," Joe Biden said. "The challenge before us right now is still immense and growing."

WASHINGTON, Nov. 9  -- Joe Biden issued a dire warning on Monday as the COVID-19 pandemic continues worsening in the United States.

"We are still facing a dark winter," Biden said from Wilmington, Delaware, as the number of COVID-19 cases in the country has topped 10 million, with 237,000 deaths. "The challenge before us right now is still immense and growing."

The Democrat went on urging Americans to wear masks.

"The goal of mask wearing is not to make your life less comfortable, or to take something away from you," he said. "It is to give something back to all of us. A normal life."

The remarks came hours after American drugmaker Pfizer and German pharmaceutical company BioNTech announced that data analysis shows their COVID-19 vaccine candidate is more than 90 percent effective in preventing COVID-19.

Biden called the news "positive" but stressed that the vaccine, even if it's approved by the U.S. Food and Drug Administration, "will not be widely available for many months yet to come."

"Projections still indicate we could lose 200,000 more lives in the coming months before a vaccine can be made available to everyone," he added.

Biden has declared victory for the 2020 presidential election, while sitting President Donald Trump hasn't conceded and is pushing for legal challenges.