President Donald Trump's campaign on Wednesday mounted challenges to vote counts in Wisconsin, which US media says Joe Biden has won, and Michigan, in which the Democrat holds a slim lead; two crucial states that could decide the election.

The Trump campaign alleged without evidence that there had been irregularities in "several" Wisconsin counties and that Michigan had not allowed the president's team to observe counting in "numerous" locations.

In Wisconsin, the Trump campaign said it had "serious doubts" about the validity of the results.  CNN and The New York Times, citing the Associated Press, have called the race in favor of the former vice president, giving him 10 more electoral votes and a total so far of 248. The magic number for victory is 270.

All votes have been counted and Biden enjoyed an edge of some 20,000 votes -- similar to Trump's margin when he won Wisconsin in 2016 over Hillary Clinton.

"The president is well within the threshold to request a recount and we will immediately do so," Bill Stepien, Trump's campaign manager, said.

Although Biden's margin was just a sliver of the more than 3.2 million votes cast in Wisconsin, Trump may have a hard time recovering that many through a typical recount.

A recount in Wisconsin during the 2016 presidential election -- requested by the Green Party after Clinton's camp decided not to pursue it -- found only 131 extra votes for Trump. "20,000 is a high hurdle," former Wisconsin governor Scott Walker, a Republican, tweeted.

The campaign also said it was taking legal action to suspend the counting of remaining votes in Michigan, where remaining ballots are largely from Democratic-leaning areas including majority African-American Detroit.

"We have filed suit today in the Michigan Court of Claims to halt counting until meaningful access has been granted," Stepien said in a statement.

"We also demand to review those ballots which were opened and counted while we did not have meaningful access. President Trump is committed to ensuring that all legal votes are counted in Michigan and everywhere else."

Michigan authorities have said they are committed to counting every note. As the campaign announced its suit, Michigan's secretary of state, Jocelyn Benson, tweeted a map of the Great Lakes state that said next to it, "Patience is a Virtue."

With Trump and Biden neck and neck across the rest of the country in electoral votes, the deciding states in their contest have come down to Arizona, Georgia, North Carolina, Nevada, Michigan, Pennsylvania and Wisconsin.

Biden at 248 electoral votes, Trump at 214

President Donald Trump and Democratic challenger Joe Biden are squaring off for what could be a legal battle for the White House, running neck-and-neck in the electoral vote count, and several battleground states still in play on Wednesday.

As it stands, there are six states still left uncalled, including major prizes such as Pennsylvania and Michigan -- meaning both Trump and Biden still have a path to victory.

US media outlets have projected wins for the Republican incumbent in 23 states including big prizes Florida and Texas, as well as Indiana, Kentucky, Missouri and Ohio -- all states he won in 2016.

Biden has captured 21 states including his home state Delaware and big prizes California and New York, as well as the US capital. The former vice president has flipped two states won by Trump in 2016 -- Arizona and Wisconsin.

Nebraska split its electoral votes between the two -- four for Trump and one for Biden. Maine was won by Biden, but he seized only three of the four electoral votes on offer, with the last allocated to Trump.

So far, that gives Biden 248 electoral votes and Trump 214. The magic number of electoral votes is 270.

The following is a list of the states won by each candidate and the corresponding number of electoral votes, based on the projections of US media including CNN, Fox News, MSNBC/NBC News, ABC, CBS and The New York Times.

In the case of Arizona, AFP used the projection made by the Associated Press.

TRUMP (214): Alabama (9), Arkansas (6), Florida (29), Idaho (4), Indiana (11), Iowa (6), Kansas (6), Kentucky (8), Louisiana (8), Maine (1), Mississippi (6), Missouri (10), Montana (3), Nebraska (4), North Dakota (3), Ohio (18), Oklahoma (7), South Carolina (9), South Dakota (3), Tennessee (11), Texas (38), Utah (6), West Virginia (5), Wyoming (3)

BIDEN (248): Arizona (11), California (55), Colorado (9), Connecticut (7), Delaware (3), District of Columbia (3), Hawaii (4), Illinois (20), Maine (3), Maryland (10), Massachusetts (11), Minnesota (10), Nebraska (1), New Hampshire (4), New Jersey (14), New Mexico (5), New York (29), Oregon (7), Rhode Island (4), Vermont (3), Virginia (13), Washington (12), Wisconsin (10)

STATES NOT YET CALLED: Alaska, Georgia, Michigan, Nevada, North Carolina, Pennsylvania

Blow to Democrats hopes to rule Senate  

Embattled Republican incumbent US Senator Susan Collins of Maine scored a come-from-behind election victory as her challenger conceded Wednesday, virtually closing Democrats' pathway to regaining control of the Senate.

Democrats saw the moderate Collins as being on the chopping block in part because of her support for President Donald Trump's Supreme Court nominee Brett Kavanaugh in 2018, and they invested heavily in her challenger Sara Gideon, who is Maine's speaker of the House.

But Collins weathered the storm, dealing a severe blow to Democratic efforts to end the 53-47 Republican majority and take back the Senate.

"I just received a very gracious call from Sara Gideon conceding the race," said Collins, who had trailed for months in polling against her Democratic rival. "I feel this is an affirmation of the work that I'm doing in Washington to fight hard every day for the people of Maine."

Collins, 67, has occasionally clashed with the president. Trump tweeted last month that there was a "nasty rumor" that Collins would not vote for his latest Supreme Court nominee, Amy Coney Barrett, and that supporting the senator's reelection effort was "not worth the work."

In October Collins indeed was the only Republican to vote against Barrett's confirmation. With some 80 percent of the vote in Maine counted, Collins was ahead by six percent -- a sharply different result than the state's presidential race, which Democrat Joe Biden won.

Gideon said in a televised address that she spoke with Collins and "congratulated her on winning this election," which chalks up another victory for Republicans from Tuesday's election.

Republicans were scrambling to defend their Senate majority and Gideon's loss now makes it that much more difficult for Democrats to win back the upper chamber of Congress. "Overall we had a better election than most people thought across the country," Senate Majority Leader Mitch McConnell, who easily won his own reelection battle, told reporters in his home state of Kentucky.

Democrats have made a net gain of just one seat so far. There are three races outstanding that Democrats could flip -- one in North Carolina and two in traditionally Republican Georgia -- but their chances for doing so are slim.

"We are in a pretty good position in North Carolina but not yet able to declare victory," McConnell said.