Trump's campaign and closely allied groups pulled in $US165 million ($A229 million) during the typically sluggish political fundraising month, disclosures revealed on Wednesday.

Democratic rival Joe Biden's generated $US140 million.

The result allows Trump to enter the final stretch of the US presidential campaign with a slim but intact cash advantage.

Trump and party-backed groups now have more than $US300 million to spend on advertisements, door-knocking organisers and other political expenses, they said, compared with Biden's $US294 million.

Democrats and Republicans will host their conventions this month.

The made-for-television pageants have been scaled back due to COVID-19 but are still expected to be watched by millions of Americans starting to pay serious attention to the long race to the White House.

The election takes place on November 3.

"The enthusiasm behind President Trump's re-election continues to grow as July's massive fundraising totals prove," said Bill Stepien, who was recently installed as Trump's campaign manager to engineer a turnaround as his poll numbers sagged under the weight of the pandemic.

The Biden campaign's money haul was near its record June number, when it beat Trump's fundraising for the second straight month.

The campaign wants to keep up that momentum as it charts a far more expansive - and expensive - effort to compete in states like Texas, Arizona and Ohio, once viewed as long-shots.

Despite falling short of Trump's number, Democrats have largely put the race on an even footing after starting with a substantial fundraising gap against Trump.

Earlier on Wednesday, Biden's campaign announced plans to spend more than $US280 million on television and digital advertising by Election Day, a figure that would all but guarantee the showdown will be the most expensive in US history.

Neither campaign's figures include the millions in fundraising being done by outside groups that support either candidate.

Australian Associated Press