Democratic presidential nominee Joe Biden and the Democratic National Committee said on Wednesday that they raised a combined $364.5 million in August, shattering the monthly record for fundraising by a presidential campaign.

The amount included more than $205 million from online, small-dollar donations, according to the campaign.

Biden, who is leading Republican President Donald Trump in most national opinion polls ahead of the Nov. 3 election, raised $140 million in July, but was outpaced by Trump and his allied groups, who raked in $165 million.

The previous monthly record - $193 million - was set by former President Barack Obama in September 2008, according to US media outlets.

Biden's haul for August is likely attributable to a number of factors, including the introduction of US Senator Kamala Harris as his running mate, enthusiasm over Biden's nomination at the Democratic convention and mounting fears among Democratic donors that the race between Biden and Trump is tightening with just two months to go.

Biden had fundraisers almost daily in August while Harris, who sought the Democratic nomination against Biden, has been able to tap into her own big-money network to boost the Democratic ticket.

The Trump campaign has yet to release its fundraising numbers for August and did not immediately respond to a request for comment.