U.S. President Donald Trump questioned the integrity of the U.S. election in his race against Democrat Joe Biden again on Tuesday, saying it would be "inappropriate" to take extra time to count the tens of millions of ballots cast by mail.

While Republican Trump, who trails in national opinion polls, cast doubt on mail-in votes, Biden offered a message of unity in two rallies in the state of Georgia as part of a foray into traditional Republican territory with a week left to go before Election Day on November 3.

Early voting, both by mail and in person, has surged to record highs as Americans have rushed to cast ballots in the election while looking to avoid exposure to the coronavirus.

The huge volume of mail ballots – more than 46 million have already been cast – could take days or weeks to tally, experts say, meaning that a winner might not be declared the night of November 3, when polls close.

"It would be very, very proper and very nice if a winner were declared on November 3, instead of counting ballots for two weeks, which is totally inappropriate and I don't believe that that's by our laws," Trump told reporters at the White House before leaving for a trip to Michigan, Wisconsin and Nebraska.

"We'll see what happens," said Trump, who has repeatedly and without evidence suggested that an increase in mail voting will lead to an increase in fraud, although election experts say that is rare in U.S. elections' history.

Trump cast an early ballot in Florida's West Palm Beach on Saturday, for himself as he revealed later.

Mail voting is a long-standing feature of American elections, and about one in four ballots was cast that way in the 2016 election.

Democratic officials, activists and voters have voiced deep anxieties that Trump will not accept the outcome if he loses. Biden has called it his biggest fear.

Democrats are voting early in greater numbers than Republicans this year, according to data from the U.S. Elections Project at the University of Florida, but some states do not allow officials to begin counting them until the polls close.

More than 69.4 million votes have been cast so far, approaching half the total 2016 votes.

Republicans in a series of court battles across the United State are trying to limit the time voters have to send in ballots.

With a week to go, Biden leads Trump nationally by 10 percentage points, according to a Reuters/Ipsos poll conducted October 23 to 27. The national online survey found that 52 percent of likely voters said they were backing Biden, while 42 percent were voting for Trump.

The race is tighter in battleground states including North Carolina, Florida and Arizona where the election might be decided. A Reuters/Ipsos poll on Tuesday showed Biden with a 52 percent - 43 percent lead over Trump in Michigan, with the two statistically tied in North Carolina.

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Unity message

Biden's visit to Georgia was a show of optimism that his campaign can end the presidency of Trump, who has overseen the ravaging of the country by the coronavirus, an increase in racial tensions and the fraying of ties with European allies.

Georgia has not supported a Democrat in a U.S. presidential election since 1992.

"I'm running as a proud Democrat, but I will govern as an American president. I'll work with Democrats and Republicans. I'll work as hard for those who don't support me as for those who do," Biden said in Warm Springs, the vacation home of former President Franklin D. Roosevelt, the Democrat who led the nation during the Great Depression and World War Two.

Later, in Atlanta, he said the fact he was campaigning in Georgia was a sign of his momentum.

"Something's happening here in Georgia and across the country," he said. "We win Georgia, we win everything."

The 2020 presidential campaign has been unlike any other as a raging coronavirus pandemic that has so far caused more than 225,000 U.S. deaths pushes record early voting.

Nearly half a million people in the United States have contracted the novel coronavirus in the past seven days, according to a Reuters tally, as cases and hospitalizations set records in hot spots in the Midwest. More than 5,600 people died from the virus nationwide in the past week.

In another show of confidence for Biden, former New York Mayor Michael Bloomberg said on Tuesday he would spend around $15 million on television advertising in Texas and Ohio in the coming days.

Later on Tuesday, Trump will visit Nebraska and Wisconsin before stopping overnight in Nevada.

Former President Barack Obama was also back on the trail in Florida on Tuesday to boost Biden, who was his vice president.

At a drive-in rally in Orlando, Obama urged Democrats to vote in large numbers to avoid a repeat of the 2016 election when Trump won the battleground state and defeated Hillary Clinton.

"We have to leave no doubt. We can't be complacent," he said. "We were complacent last time. Folks got a little lazy, folks took things for granted, and look what happened. Not this time, not in this election," he said.

(With input from Reuters)