President Donald Trump held an in-person rally in Pennsylvania, a day after a new poll showed a tightening race between him and his Democratic rival Joe Biden, in the battleground state.

Addressing a crowd of supporters inside a hangar at the Arnold Palmer Regional Airport in Latrobe, Trump on Thursday night claimed what he believes are achievements of his first term, speaking from economy to space programs, and sought to highlight ideological and policy differences between his administration's and those of Democrats, reports Xinhua news agency.

He continued to stress a "law and order" message, as the country has been further divided by a series of police-involved incidents that led to several deaths and triggered nationwide demonstrations subsequently.

"I'll bring rioters, looters, violent extremists, anarchists -- we will bring them to justice, that's what we're doing right now...

"We are taking back America from these very, very deranged people," Trump said amid criticism from Democrats that his remarks have been sowing chaos for political benefits.

The President claimed that mail-in voting would cause massive voter fraud as states have moved to expand access to it amid the coronavirus pandemic.

Additionally, he talked at length about his physical conditions last November, dismissing previous reports which claimed that he had had "mini-strokes".

Biden, in a statement responding to the President, accused Trump of not taking "responsibility for the economic hardship his presidency has caused Pennsylvanians".

"But even before this crisis began, President Trump's reckless economic policies and tariff wars shipped jobs overseas and lined the pockets of CEOs, while leaving Western Pennsylvania workers and families behind," the 2020 Democratic presidential nominee said.

"Wall Street didn't build this country, the middle class built this country."

The former Vice President added that if he's elected he will "fight for hardworking Pennsylvanians, bring our economy back from the brink, and create good-paying, manufacturing and union jobs".

The remarks came exactly two months before the Election Day and a day after the latest Monmouth University survey found Biden at 49 per cent and Trump at 45 per cent among all registered voters in Pennsylvania.

That number was within the poll's 4.9-point margin of error and a far closer race than Monmouth found in July, when Biden led 53 to 40 among registered voters.

"This is really a game of inches," said Patrick Murray, director of the independent Monmouth University Polling Institute.

"The Trump campaign is looking to peel off a little bit of Biden support here and a little bit there.

"It may be working, despite the fact that Pennsylvania voters personally like the Democrat more, although this gap has narrowed," Murray added.

According to the poll, Trump led by 19 points among men in Pennsylvania, compared to his 2-point advantage in July, while Biden was 24 points ahead of his Republican opponent among women and by 11 points among seniors.

Trump won Pennsylvania, which had voted Democratic in six consecutive presidential elections prior to 2016, by less than one percentage point, against then-Democratic presidential nominee Hillary Clinton.

He also won Michigan and Wisconsin, two other states dubbed as the "blue wall" four years ago.

Trump needs to win in at least two of those states if not all three for his re-election.

According to the polling average of RealClearPolitics, a political news site and polling data aggregator, Biden is still ahead of Trump by 7.2 percentage points nationally and 3.3 points in top battleground states.

Trump has repeatedly called polls showing him trailing Biden "fake" and said that his voters have been "suppressed".

Biden, who was born in Scranton, Pennsylvania in 1942 and spent his first 10 years there before moving with his family to eastern state of Delaware, has retained strong ties to the Keystone State.

The Democratic political veteran formally kicked off this presidential campaign in Philadelphia last May.

In the past few weeks, he has held several campaign events in the state, including a speech Monday in Pittsburgh, which is about an hour of drive from Latrobe.