Donald Trump’s momentum in latest opinion polls forced Hillary Clinton to campaign in states that had been considered safe for the Democrats.
Both teams are now concentrating more on getting their supporters to vote, rather than swaying those undecided.
Thirty-seven million early ballots have already been cast.
Meanwhile, authorities say they are assessing the credibility of information on a possible al-Qaeda terror attack.
New York, Texas and Virginia are believed to be the potential targets mentioned in connection with a possible attack before Election Day on November 8, but a police spokesman said the information “lacks specificity”.
Officials say they regularly assess all possible threats before major events.
News of a possible attack came as both Hillary Clinton and Donald Trump made final pushes for support in battleground states across the US.
They both held rallies in Ohio and Pennsylvania on November 4, two states that may prove crucial on the Election Day.
Both candidates are due to campaign in Florida on November 5. Florida is seen as a key contest that could tip the election.
In Cleveland, Ohio, Hillary Clinton ended the day’s campaigning at a concert, where she was joined by Beyonce and Jay-Z.
“We have unfinished work to do, more barriers to break, and with your help, a glass ceiling to crack once and for all,” Hillary Clinton said.
Addressing the crowd, Jay-Z explained his support for Hillary Clinton. The rapper said that though he did not have any “ill will” towards Donald Trump, the Republican’s conversation was “divisive”.
“That’s not an evolved soul to me, so he cannot be my president. He cannot be our president,” the rapper said.
The free concert was part of a series of events put on by Hilalry Clinton’s campaign as she aims to encourage greater African-American participation in the election.
Donald Trump, meanwhile, told a crowd of supporters in New Hampshire that his rival wants a “550% increase” on Syrian refugees allowed into the US.
“Her plan would mean generations of terrorism, extremism, and radicalism spreading into our schools and communities,” the Republican nominee said.
Earlier, at a rally in Pittsburgh, Pennsylvania, Hillary Clinton said that her opponent was “unfit” for office because of his temperament and disparaging comments about women and minorities.
Donald Trump is currently ahead in Ohio, according to a state polling average by Real Clear Politics (RCP), while Hillary Clinton leads by a small margin in Pennsylvania.
In Florida, RCP’s poll average puts Hillary Clinton ahead, but poll analysis website FiveThirtyEight says Donald Trump has a 52.4% chance of winning the state’s 29 electoral votes.
National polls have suggested that Donald Trump has gained substantial ground on his rival in the last week or so. That momentum also appears to have helped Donald Trump in several key battleground states.