Trump has complained on the election campaign hustings about the federal response to natural disasters that have damaged much of the southeast as he seeks to gain a political advantage from two recent hurricanes.
Speaking at the White House on the government's work to address Hurricanes Milton and Helene, Biden condemned the "reckless, irresponsible and relentless disinformation and outright lies that continue to flow".
The White House, and Biden personally, have spent days decrying Trump for making false claims about the disaster response, including that federal funding is being diverted for use on people in the country illegally and that such assistance is capped at $750.
The $750 is an immediate need disbursement, Biden explained, to cover urgent requirements like food, diapers and baby formula.
"That $750 that they're talking about, Mr Trump and all those other people know it's a lie to suggest that's all they're going to get," Biden said.
"It's just bizarre. They got to stop this. They're being so damn un-American with the way they're talking about this stuff."
Hurricane Milton ravaged Florida on Wednesday, whipped up a barrage of tornadoes and caused at least five deaths.
The region was still reeling two weeks after Hurricane Helene flooded streets and homes in western Florida and left at least 230 people dead.
The former president Trump spoke at the Detroit Economic Club after holding rallies in Pennsylvania on Wednesday.
Trump sent a message to people affected by Hurricane Milton and Hurricane Helene.
He praised Republican governors of Florida, Georgia and South Carolina but suggested the federal response had been lacking, particularly in North Carolina, where he alleged the government after Helene had "not done what you're supposed to be doing".
"They've let those people suffer unjustly," said Trump, who has for several days promoted falsehoods about the response of Biden and emergency management officials.
Vice President Kamala Harris is set to attend a Univision town hall in Las Vegas and an evening rally in Phoenix while remaining in close contact with the White House and monitoring federal disaster response efforts.
President Joe Biden, who said Milton "is looking like the storm of the century," postponed a trip to Germany and Angola to cope with its aftermath.
He and Harris were huddling with top officials in the Situation Room to discuss disaster response.
Former President Barack Obama will have a cameo appearance on the Harris campaign. (AP PHOTO)
Meanwhile, former President Barack Obama is also hitting the campaign trail on Thursday night, making his first appearance for Harris at a rally in Pittsburgh.
That begins what the Harris campaign says will be a series of campaign stops Obama will make on the vice president's behalf.
Biden spent Monday campaigning in suburban Philadelphia, but has made just one joint appearance with Harris, joining her in Pittsburgh on Labor Day, since he announced he was leaving the race and endorsing her in July.
Obama was among the key Democrats who were part of a behind-the-scenes effort to encourage Biden, his former vice president, to drop out.
Obama and Harris have also been friends for two decades, since he ran for Senate in Illinois. She campaigned for him when he sought the presidency in 2008.
