The CNN, NBC broadcasters and AP news agency declared the Democrat nominee's win on Saturday.

As per them, Mr Biden has crossed the 270 electoral votes-mark.

CNN said Pennsylvania's 20 electoral votes put Biden over the 270 electoral votes needed to win.

With Pennsylvania in his kitty, Biden has now got 273 out of 538 Electoral College votes, crossing the 270-limit, dashing all hopes of Donald Trump to secure a second term even if he managed to win the rest of the undeclared states.

The vote counting in Pennsylvania was still in progress.

The former two-term vice-president and a Senate vetera -- Biden, will be the 46th President of the United States.

According to reports, incumbent President Donald Trump had no immediate reaction to the news.

After the win, Biden tweeted: "America, I’m honored that you have chosen me to lead our great country. The work ahead of us will be hard, but I promise you this: I will be a President for all Americans — whether you voted for me or not. I will keep the faith that you have placed in me."

Harris, a senator and former California attorney general, will also enter the White House to become the first Black and South Asian Vice-President and also the first woman to hold the post.

Soon after the declaration, the 56-year-old wrote on her Twitter handle, "This election is about so much more than @JoeBiden or me. It’s about the soul of America and our willingness to fight for it. We have a lot of work ahead of us. Let’s get started."

Harris also tweeted a video of herself congratulating Biden on his winning the presidency and the success of their campaign. The CNN said the video was taken by her husband Doug Emhoff, according to a Harris aide.