Here is what we know about the states where the outcome of the US election is proving difficult to predict:

Florida

Florida is one of the pivotal states in the vote.

Advisers of Republican hopeful Donald Trump have previously said he must win this southeastern state.

As it stands, there are fewer than 150,000 votes in it.

Georgia 

A key battle is being fought out in Georgia, a majority white state.

Democratic President Bill Clinton won here in 1992 but not in 1996, while Barack Obama failed to ever enjoy a victory in the state, which is bordered to the south by Florida.

New Hampshire 

In this northeastern swing state, results have often varied. In 2000, the state voted Republican, but since 2004 residents have opted for the Democrats.

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Trump is the first Republican in 100 years not to win the endorsement of the state's right-wing flagship newspaper, the Manchester Union Leader.

Clinton has led consistently but is by no means a certain winner.

North Carolina 

The African-American vote is key here, and could prevent a victory for the Republicans in the state. However, there are claims that their vote has been suppressed.

In 2012, North Carolina voted Democrat, but in 2004 and 2000 it was Republican.

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For the past four elections, North Carolina has voted for the candidate who became president.

Ohio

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In this eastern state, more than 80 percent of residents are white. It has voted for the winning party in each presidential election since 1964. No Republican candidate has won without it. Trump hopes that his anti-globalism message will resonate in this former industrial powerhouse, which has lost out on trade deals as of late.

Pennsylvania

Pennsylvania has been called the "biggest firewall state" by analysts, and Clinton has maintained a healthy lead in the state ahead of the elections. Republicans have not won this state since 1988. But while polls have shown Clinton with a fairly comfortable lead, Pennsylvania is historically a major swing state and its 20 electoral votes make it a big win.

Virginia

In this state on the East Coast, African-Americans account for one in five votes. Clinton has been up in the polls for most of the campaign. But as it stands, Trump is doing better than expected.

Michigan

This hard-fought midwestern state drew both the Democratic nominee and Obama on the campaign's final day. Other big names to visit the state on Monday were Mike Pence, Chelsea Clinton, and Trump's children - Donald Junior and Ivanka. 

Maine

With little more than 1 percent of black residents, turnout in Maine was expected to be high. It is one of five states deciding on recreational marijuana on election night. For the first time in history, Maine could split its four electoral votes. Trump's team has visited several times over the past two months.

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Source: Al Jazeera News