ERIE, PENNSYLVANIA (BLOOMBERG) - Mr Joe Biden sowed doubt about the integrity of the presidential election by suggesting Saturday (Oct 10) that the only way he can lose is if there's "chicanery" at polling stations.

"Make sure you vote. Because the only way we lose this is by the chicanery going on relative to polling places," the Democratic presidential nominee told supporters in Erie, Pennsylvania.

Mr Biden later told reporters that "I'm going to accept the outcome of this election, period" and said he was referring to "attempts that are made to try to influence and scare people from voting."

It was a line that echoed US President Donald Trump's repeated efforts to question election integrity.

The president, who's trailing Mr Biden in most national and battleground state polls, has suggested without evidence that mail-in ballots are subject to widespread fraud, and is preparing to potentially challenge results that don't go his way.

"The only way we're going to lose is if there's mischief," Mr Trump said last month.

Mr Biden has been urging his supporters to vote in numbers that give him a clear victory so that Mr Trump has no grounds to contest the outcome.

"The American people are voting and they're voting in large numbers," Mr Biden told reporters, saying his earlier remark was taken out of context.

"They're going to determine the outcome and I'm going to accept the outcome of the election without any question."

But the former vice-president's comments Saturday came off as a warning about bad things happening at polling places - the same kind of warning for which he's chastised Mr Trump.

At a fundraiser in July, Mr Biden warned of the potential for "chicanery" and said his campaign had built a network of lawyers to fight for the integrity of the election.

In a September Facebook post, Mr Donald Trump Jr, the president's son, urged "able-bodied" supporters to join an "army for Trump's election security."

Mr Biden spoke in Pennsylvania hours after a district judge there rejected the Trump campaign's challenge to the state's vote by mail procedures, as well as the campaign's attempt to allow poll watchers who don't live in the county they want to monitor.

Separately, Pennsylvania Republicans are asking the US Supreme Court to require that all mail-in ballots in the state be counted by Election Day.