WASHINGTON, United States (AFP) – Just two days before the bitter US presidential election, national polls gave the edge to Hillary Clinton, with results too close to call in some key battleground states where the race will be won or lost.

A final NBC/WSJ poll showed the Democratic White House hopeful with a four-point lead ahead of her Republican counterpart Donald Trump, at 44 to 40 per cent in a four-way national survey out Sunday.

“If you only have 44 per cent of the vote that means you’re vulnerable if most of the undecideds break in a certain way,” pollster Nate Silver of the news website FiveThirtyEight.com told ABC’s “This Week.”

“In that sense both candidates still need a good turnout on election day and still have their work cut out for them,” Silver said.

That was nowhere more apparent than in Ohio and Florida polling results out Sunday, where CBS News Battleground Tracker polls showed Clinton’s lead evaporating.

CBS gave Trump a one point lead in Ohio (46 to 45 per cent) and showed a tied race in Florida (45 to 45 per cent).

Florida is the mother of all swing states, with 29 electoral votes in the electoral college, where a victor must reach 270 votes to win the presidency.

The Tuesday election could hinge on roughly a dozen so-called battleground states where the contest is particularly tight.

Trump and Clinton have packed their last-minute schedules with campaign events, particularly in swing states, hoping to woo voters in the final 48 hours of a race that is too close to call.

“The electoral college map is less solid for Clinton than it was for (President Barack) Obama four years ago,” Silver said.

“You’d rather be in her shoes than Donald Trump’s but it’s not a terribly safe position,” he added.

As of Sunday his website gave Clinton a 64.2 per cent chance of winning the race.

Meanwhile polling aggregates by tracker RealClearPolitics showed Clinton in the lead with 46.6 per cent to Trump’s 44.8 per cent.