WASHINGTON — Democrat Joe Biden leads in the national polls and most of the battleground states going into Election Day, but US President Donald Trump is insisting they're wrong and he'll repeat his upset victory of 2016.

Mr Biden, the 77-year-old former vice president, has enjoyed a solid lead over Mr Trump, 74, in the national polls for months, at times reaching double digits.

But US presidential elections are not decided by the popular vote.

They are won in the 538-member Electoral College, where each state has a number of electoral votes equivalent to its representation in the House and Senate.

And the electoral votes of battleground states such as Florida and Pennsylvania could determine the winner of Tuesday's battle for the White House.

Here is a look at the latest national polls and polls in key battleground states:

NATIONAL POLLS

An average of national polls by the RealClearPolitics (RCP) website gives Mr Biden a 6.8 point lead over Mr Trump — 50.7 per cent to 43.9 per cent.

That is roughly in line with the averages of other leading outlets such as FiveThirtyEight.com, which has Mr Biden up by 8.4 points nationally.

Mr Biden's lead nationally is more than double that of Hillary Clinton going into the 2016 election, when the polls were relatively accurate concerning the popular vote, which she won while losing in the Electoral College.

FLORIDA

In Florida, Mr Biden has a 1.7 point lead over Mr Trump, according to the RCP average of state polls.

A Siena College/New York Times poll has Mr Biden up by three points in the Sunshine State but a Washington Post/ABC News poll has the Republican incumbent up by two points.

Mr Trump won Florida and its 29 electoral votes in 2016 and winning the state again is seen as crucial to his hopes of victory.

PENNSYLVANIA

In Pennsylvania, Mr Biden has a 2.9-point lead, according to the RCP average of polls in the Keystone State, which has 20 electoral votes.

Mr Trump won Pennsylvania by just 44,000 votes in 2016 and his reelection hopes could hang on taking the state again. 

MICHIGAN, WISCONSIN

Michigan and Wisconsin are two Midwestern states Mr Trump won narrowly in 2016 but the RCP averages have him trailing in both this time.

According to the RCP averages, Mr Biden is up by 5.1 points in Michigan, which has 16 electoral votes, and by 6.6 points in Wisconsin, which has 10 electoral votes.

ARIZONA, NORTH CAROLINA

The battleground states of Arizona and North Carolina, both of which Mr Trump won in 2016, are also being closely watched.

According to the RCP averages, Mr Biden has a 0.5 point lead in Arizona, which has 11 electoral votes, while Mr Trump leads by 0.5 points in North Carolina, which has 15 electoral votes.

GEORGIA, IOWA, OHIO, TEXAS

Four other states are also being closely watched this time — Georgia (16 electoral votes), Iowa (six), Ohio (18) and Texas (38).

Mr Trump won all four states relatively easily in 2016 but the polls are showing close races there this time.

Mr Trump is up by 0.2 points in Georgia, according to the RCP average, a state Mr Trump won by 5.1 points in 2016.

Mr Trump is up by 1.4 points in Iowa — he won by 9.4 points four years ago — and by 1.4 points in Ohio, a significantly smaller margin than his 8.1-point win last time around.

Mr Trump won Texas, one of the biggest prizes of the night, by nine points in 2016 but the RCP average gives him a narrow 1.2 point lead there ahead of Tuesday's vote. AFP