WASHINGTON • Voters in the crucial battleground states of Michigan, Pennsylvania and North Carolina will begin casting ballots for the US presidential election in September, giving President Donald Trump and his rival Joe Biden just weeks to argue their cases.

The first absentee ballots will be sent out in North Carolina starting on Sept 4. Voters in Pennsylvania will be able to request, fill in and turn in absentee ballots in person starting on Sept 14, followed by voters in Michigan on Sept 19.

That could spell trouble for Mr Trump, who is behind the Democratic nominee in national polls as well as the most recent polls in all three states.

Mr Lon Johnson, former chair of the Michigan Democratic Party, said early voting would force Mr Trump and Mr Biden to make their "closing arguments" much sooner than in previous years.

"In the past, campaigns had a three-week window before the election where it was crunch time," he said. "That window has expanded significantly."

In 2016, more than 47 million voters cast their ballots before election day, either in person or by mail, according to an accounting by Dr Michael McDonald of the University of Florida.

Election administrators are encouraging voting even earlier this year to avoid problems at the polls and to ensure their votes are counted during the pandemic.

"Early voting is definitely a part of the solution to Covid-19," said Mr Don Palmer, a Trump-appointed member of the US Election Assistance Commission.

"If you're going to vote absentee or mail, it is always good from my perspective to start early, and make that request, because often you'll have a process where you are dealing with the bureaucracies of the post office or the election office."

Early voting has also compressed the election calendar. North Carolina will begin mailing ballots out just eight days after the Republican National Convention ends late next month, while voters in all three states will be able to cast a ballot before the first presidential debate on Sept 29.

BLOOMBERG