US singer-actress Cher performs a song during a voter mobilization event for supporters of Democratic presidential candidate Joe Biden in Las Vegas on Saturday. Photo: AFP

An energized Joe Biden and Barack Obama Saturday accused Donald Trump of a massive screw-up in his handling of coronavirus, but the US president remained ebullient despite trailing in polls with 10 days to go until the election.

Trump plowed through three campaign rallies in one day, targeting separate battleground states as he sought to close the gap with Biden.

But the president's efforts have been inescapably overshadowed by a grim reality: The US set a daily record for new COVID-19 cases for the second day in a row on Saturday, at nearly 89,000, with a further surge expected as cold weather arrives.

The virus has claimed more than 224,000 American lives, with no end in sight, and a majority of voters say Trump has handled the crisis poorly.

"That's Donald Trump's presidency," Biden said Saturday during a drive-in rally, one of two events in his native Pennsylvania, a critical swing state. He spoke from a stage decorated with bales of hay and Halloween pumpkins.

"Donald Trump said, and is still saying, we're rounding the corner. It's going away. We're learning how to live with it." Biden said. "We're not learning how to live with it. You're asking us to learn how to die with it and it's wrong."

The Biden campaign also deployed a key surrogate, former president Barack Obama, who slammed the Trump administration's COVID-19 response.

"The idea that somehow this White House has done anything but completely screw this thing up is nonsense," Obama told supporters at a drive-in rally in Miami, Florida.

"Donald Trump isn't suddenly going to protect all of us. He can't even take the basic steps to protect himself," Obama added, referring to Trump's hospitalization for COVID-19 three weeks ago.

Also slamming the president's failure to denounce white supremacy, and the many times he has lied in public, among other issues, Obama called on supporters to vote for his former vice president.

AFP