President Donald Trump and rival Joe Biden were courting early voters on Sunday in the competitive states of Nevada and North Carolina, as the final presidential debate looms later this week.

Both men are working to rouse their political bases and appeal to the seemingly small number of undecided voters in an election that could revolve around voter turnout.

One key opportunity comes this week with the candidates' final nationally televised debate, on Thursday evening in Nashville, Tennessee.

Some 27.7 million Americans have already cast ballots either by mail or in-person ahead of the November 3 election, according to the U.S. Elections Project at the University of Florida. The record-shattering figure is being driven in part by concerns about crowds at polling sites on Election Day amid the coronavirus pandemic.

In North Carolina, a battleground where 1.4 million, or 20 percent, of the state's registered voters, had already voted as of Sunday morning, Biden urged residents to cast ballots as soon as possible. "We gotta keep the incredible momentum going; we can't let up," he said at a "drive-in rally" in Durham, as attendees sitting in their cars honked in approval. "Don't wait - go vote today."

Biden also criticized Trump for saying over the weekend that the U.S. had "turned the corner" in the coronavirus pandemic, noting that the rate of new cases across the country has risen to the highest level in months.

"As my grandfather would say, 'This guy's gone around the bend if he thinks we've turned the corner,'" Biden said. "Things are getting worse, and he continues to lie to us about circumstances."

Biden's pick for vice president, Senator Kamala Harris, canceled in-person events over the weekend as a precaution after an aide tested positive for COVID-19. She will return to the campaign trail on Monday with a visit to Florida to mark that state's first day of early in-person voting.

Harris tested negative for the virus on Sunday, the campaign said.

Trump, a Republican, was spending his Sunday in Nevada, a state he hopes to wrest away from Democrats after narrowly losing it in 2016. Early in-person voting in the state began on Saturday.

The president, who rarely goes to church but has remained popular among evangelical Christians for his opposition to abortion and for appointing conservative judges, began his day by attending a service at the International Church of Las Vegas.

Trump, who recently came down with his own bout of COVID-19, did not wear a mask for the indoor service.

One of the church's pastors, Denise Goulet, said to Trump from the stage that God had told her he would win the 2020 election. Trump put a handful of 20 dollars bills into an offering bucket and bowed his head during a prayer.

Trump will campaign every day leading up to Thursday's debate in Florida, including stops in Arizona and North Carolina, campaign spokesman Tim Murtaugh said.

While Trump lags in opinion polls at a national level and in many battleground states, Biden campaign manager Jen O'Malley Dillon said over the weekend that the national figures are misleading because must-win states are close.

"We cannot become complacent because the very searing truth is that Trump can still win this race, and every indication we have shows that this thing is going to come down to the wire," she wrote in a memo to donors.

U.S. presidential elections are determined by electoral votes, allotted to U.S. states and territories based largely on their populations, rather than by a tally of the popular vote nationwide.

Trump campaigned on Saturday in Michigan and Wisconsin, two battleground states he narrowly won in the 2016 election.

In Muskegeon, Mich., he attacked Michigan Governor Gretchen Whitmer, a Democrat, for imposing restrictions to slow the spread of the coronavirus and made light of a right-wing plot uncovered by the FBI to kidnap her.

"Hopefully you'll be sending her packing pretty soon," Trump said, prompting the crowd to yell back "Lock her up!" several times.

Whitmer said on Sunday's "Meet the Press" on NBC that the president's rhetoric was "incredibly disturbing" and "dangerous" for her and her family as well as other politicians whom he targets.

(With input from Reuters and AFP)