WHITE HOUSE - U.S. President Donald Trump and his election challenger, former Vice President Joe Biden, on Thursday accused each other as being unfit for office.

Trump, who is 74, characterized his 78-year-old opponent as "shot" and "weak" and alleged that "something is off" with Biden's mental state.

Speaking at a political rally in the Midwestern state of Wisconsin, 47 days before the election, the Republican president added that Biden "doesn't know he's alive."

Biden, in Pennsylvania, criticized Trump as being "totally irrational" in his handling of the coronavirus pandemic and discouraging people from following the scientific advice of the government's own health experts.

"You've got to level with the American people - shoot from the shoulder," said Biden. "The president should step down."

If Trump had acted earlier, he would have saved thousands of American lives from the coronavirus, according to Biden.

"He knew it and he did nothing," Biden said. "It's close to criminal."

"I've been doing this a long time. I never, ever thought I would see such a thoroughly, totally irresponsible administration," said Biden.

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While Biden was still at the drive-in event organized and broadcast live by CNN from the parking lot of baseball stadium in Moosic, Pennsylvania, Trump took to the podium at an airport in Mosinee, Wisconsin, with Air Force One as his backdrop.

Both Pennsylvania and Wisconsin are battleground states for the November 3 election.

In recent weeks in Pennsylvania, polls have shown Trump closing the gap with Biden, who still holds approximately a lead of 4 percentage points.

In Wisconsin, an average of major recent polls indicates Biden leading Trump by nearly 7 points.

Trump, speaking to an estimated crowd of 1,000 people, quickly made note of Biden's event, which overlapped his, creating a split screen moment for political junkies.

"He's up there tonight getting softball questions from (program host) Anderson Cooper," said the president. "They don't ask me questions like that."

Trump hurled insults throughout his 90-minute rally at the former vice president and the Democratic Party nominee's running mate, U.S. Senator Kamala Harris.

"Wait till you see what (Vice President) Mike Pence does to her in the debates," said Trump.

Pence and Harris are scheduled to face off in one debate of the vice-presidential candidates in Salt Lake City, Utah on October 7.

Trump and Biden are to spar in person three times before the November election. Their first debate will be on September 29 in Cleveland, Ohio.

"I have gone back and talked about and looked at not only the things he said, but making sure I can concisely say what I'm for and what I'm going to do," Biden said about his preparation for the debates.

Biden said there is not yet a person in his campaign playing Trump for the debate preparation.

"There are a couple of people, they ask me questions if they were like as if they were President Trump," said the former vice president. "But I'm looking forward to it."

Trump, earlier this week, when asked how we was getting ready for the encounters with Biden said he is following his normal routine "by just doing what I'm doing."

Patsy Widakuswara in Mosinee, Wisconsin, contributed to this story.