Trump says it's "amazing how the mail-in ballots are so one-sided".

Democrats are known to use postal voting more - in fact so far approximately 75% of postal votes have been for Joe Biden.

Trump ran a campaign based on false claims that postal voting was more vulnerable to fraud, and encouraged his supporters not to vote by post.

• Do postal ballots lead to voting fraud?

The president tells the news conference that there's "a lot of litigation because of how unfair this process was". Most of the cases have been launched by his campaign to stop counting in battleground states.

• Could the election be decided in courts?

Adding to his unsubstantiated claims of electoral fraud, Trump claims the media's polling before the vote was "election interference".

Trump tells reporters: "There was no blue wave, as predicted, instead there was a red wave" - referring to the colours of the Democratic and Republican parties respectively.

Speaking on the congressional elections, which also happened on Tuesday, Trump says: "More Republican women were elected to congress than any year before."

He then adds that Republicans have become 'the party of the American worker".

Donald Trump, addressing a news conference at the White House, says: "If you count the legal votes I easily win."

Trump has made the claim before, even though votes are still being counted. Moreover, these are not "illegal" votes - but legitimate mail-in ballots that are now being counted.

• The most viral US vote claims debunked

The president has started his news conference.

We reported earlier that the Trump campaign had filed another lawsuit in Pennsylvania, claiming that Republican representatives have been barred from attending ballot counts.

Now, a Philadelphia federal judge has scheduled an emergency hearing on the suit.

According to New York Times reporter Alan Feuer, the hearing will take place on Thursday night.

This is just one of several lawsuits Trump has filed to try to stop vote-counting in key states. You can read more about these here.

As vote counting continues in key states, the president has repeated unsubstantiated claims of fraud and his campaign is challenging several state tallies in court.

A senior campaign official told CBS that Trump would not concede just because Biden declares victory.

Meanwhile his son Donald trump Jr urged his father to "go to total war over this election", in a post flagged by Twitter as misleading.

The official overseeing elections in Pennsylvania, Kathy Boockvar, told reporters that "very strong processes" were in place to ensure that ballots are accurately and securely counted.

She said the mail-in voting system involved "the same process that we have used for decades for absentee voting".

"The strength of the integrity of this vote is really unparalleled," she added.

Boockvar said she could not estimate when the count would be complete: "That means it's going to take longer to actually see who winner is."

We know there are about 326,000 postal votes left to count in Pennsylvania - but do we know how many of those could be for Biden?

As the BBC's Paul Danahar points out, so far about 75% of postal votes have been for Biden, because that's how he encouraged his supporters to vote.

At the same time, Trump held a campaign in the summer falsely claiming that postal voting was vulnerable to fraud.

So if 75% of the remaining postal votes in Pennsylvania are for the Democrats, that could hand Biden another almost 250,000 - giving him the state's 20 electoral votes, and the presidency.

President Trump is due to address the country from the White House at 18:30 EST (23:30 GMT), the press secretary has just announced.

While all eyes are on Pennsylvania, with the state's top election official delivering an important update on the count there, Trump's lead is shrinking.

Just before noon local time, he had a lead of 132,611 votes in the state - but as of 17:30 (22:30 GMT), this had shrunk to 90,542.

This means that Biden has cut into Trump's margin by more than 40,000 votes in less than six hours.

Kathy Boockvar says the overwhelming majority of ballots will be counted by Friday. Pennsylvania's top election official adds that late-arrival ballots are "significantly lower" than expected.

Kathy Boockvar adds that she is not aware of any recent allegations of voter fraud in the Pennsylvania vote.

Several hundred thousand votes remain to be counted, says the Pennsylvania secretary of state.

The official overseeing elections in Pennsylvania, Kathy Boockvar, says it will take a while longer to see who has won in the state.

"The counties are continuing to count. It's very close in Pennsylvania, no question. It's going to take longer to see who the winner is."

Image source, Reuters

The briefing by the Secretary of State Kathy Boockvar begins.

President Trump is not planning to throw in the towel simply because Joe Biden declares victory, CBS reports, quoting a senior Trump campaign official.

“In a free and fair election, the president will win,” CBS quotes the official as saying.

We've reported previously that Donald Trump is taking legal action over vote counting in several key states.

Now, Trump appears to have filed another lawsuit in Pennsylvania that claims Republican representatives are being denied access to the ballot count there.

Buzzfeed reporter Zoe Tillman has tweeted the full complaint.

Trump has made unsubstantiated claims of victory and accused Democrats of trying to "steal the election".

Joe Biden is currently leading in Nevada and Arizona, and as counting continues in Georgia and Pennsylvania, the gap is closing between Trump and him there.

You can read more about Trump's lawsuits here.