US polls on knife edge

Democrat Joe Biden edged closer to victory over President Donald Trump in the US presidential race on Thursday as election officials tallied votes in the handful of states that will determine the outcome, report agencies.

Vote counters worked all night in the crucial states that will decide the cliffhanger election with margins narrowing in Arizona, Georgia and Pennsylvania as former Vice President Joe Biden edged toward the 270 electoral votes needed to win and President Donald Trump pinned his hopes on a more uphill route back to the White House.

Biden currently leads with 253 electoral votes to Trump's 213. The race is coming down to tight vote counts in Arizona, Georgia, Nevada and Pennsylvania.

If the former vice president wins Pennsylvania, the race will be over. Thousands of mostly mail-in votes remain uncounted so far, with Biden trailing by just more than 135,000 votes.

The Democratic nominee has also been making a run in Georgia, which has 16 electoral votes, where the President's lead dwindled to about 18,500 votes overnight.

The story was reversed in Arizona, where several tranches of votes from Maricopa County, which includes Phoenix, narrowed Biden's lead to just under 69,000 votes with Trump's team insisting the President will eventually prevail and keep his hopes of a path to 270 alive.

There is also a close contest in Nevada, which released very little information on Wednesday with an estimated 200,000 ballots outstanding.

The Republican president, who during the long and rancorous campaign attacked the integrity of the American voting system, has alleged fraud without providing evidence, filed lawsuits and called for at least one recount.

Trump had to win the states where he was still ahead, including North Carolina, plus either Arizona or Nevada to triumph and avoid becoming the first incumbent US president to lose a re-election bid since fellow Republican George HW Bush in 1992.

The president appears to have grown more upset as his leads in some states have diminished or evaporated during the counting. On Thursday morning, he weighed in on Twitter, writing, "STOP THE COUNT!"

The knife-edge US presidential race tilted toward Democrat Joe Biden early Thursday, with wins in Michigan and Wisconsin bringing him close to a majority, but President Donald Trump claimed he was being cheated and went to court to try and stop vote counting.

Both candidates still had paths to winning the White House by hitting the magic majority threshold of 270 of the electoral votes awarded to whichever candidate wins the popular vote in a given state.

But momentum moved to Joe Biden, who made a televised speech from his hometown of Wilmington, Delaware to say that "when the count is finished, we believe we will be the winners."

To reach 270, he was hoping next to add the six electoral votes from Nevada, where he had a small and shrinking lead, or, even better, the larger prizes of hard-fought Georgia or Pennsylvania.

On Wednesday, President Donald Trump's campaign filed lawsuits in Pennsylvania, Michigan and Georgia, laying the groundwork for contesting battleground states.

The new filings, joining existing Republican legal challenges in Pennsylvania and Nevada, demand better access for campaign observers to locations where ballots are being processed and counted, and raise absentee ballot concerns, the campaign said.

The Trump campaign also is seeking to intervene in a Pennsylvania case at the Supreme Court that deals with whether ballots received up to three days after the election can be counted, deputy campaign manager Justin Clark said.

The actions reveal an emerging legal strategy that the president had signaled for weeks, namely that he would attack the integrity of the voting process in states where the result could mean his defeat.

His campaign also announced that it would ask for a recount in Wisconsin, a state the AP called for Biden on Wednesday afternoon. Campaign manager Bill Stepien cited "irregularities in several Wisconsin counties," without providing specifics.