Donald Trump savaged US media Thursday for reporting claims that he groped and forcibly kissed women -- allegations he insisted were "outright lies" -- as First Lady Michelle Obama blasted the Republican nominee in a campaign trail tirade.

With just 26 days until Americans choose a successor to her husband on November 8, a visibly angry Obama delivered a fiery takedown of the real estate mogul and his "disgraceful" behavior.

"Now is the time for all of us to stand up and say, enough is enough," Obama told a rally for Hillary Clinton in New Hampshire. "This has got to stop right now."

But the 70-year-old billionaire was not cowed, castigating his accusers as "horrible liars" and decrying his Democratic rival as complicit in a coordinated media attempt to sabotage his campaign.

Claims by at least six women have come to light in accounts reported by The New York Times, NBC, People Magazine and other outlets, most of them after Trump asserted in Sunday's debate with Clinton that he never sexually assaulted women.

Trump's accusers countered that statement, saying he made unwanted physical advances against them.

With his campaign in free-fall, Trump lashed out in battleground Florida, denying the alleged incidents occurred.

"These vicious claims about me of inappropriate conduct with women are totally and absolutely false. And the Clintons know it very well," Trump told a rally in West Palm Beach. "They're pure fiction. And they're outright lies."

The attacks, he added, "are orchestrated by the Clintons and their media allies."

Trump said his lawyers were preparing a lawsuit against The New York Times -- which published the accounts of two women who accused him of groping and kissing them -- unless the paper retracts the article.

The Times refused to back down.

"We published newsworthy information about a subject of deep public concern," and Americans are entitled to hear the women's claims, the paper's assistant general counsel David McCraw said in a letter to Trump's lawyers.

"If Mr Trump disagrees... we welcome the opportunity to have a court set him straight."

- 'Disgraceful, intolerable' -
The women's accusations surfaced days after a video emerged of Trump boasting in 2005 that his fame allowed him to grope women with impunity, sending the White House race into unprecedented levels of vulgarity.

He has apologized and, trying to reverse his deficit in national polls to the 68-year-old Clinton, sought to minimize the comments as "locker room talk" -- a remark that went too far for the first lady.

"This wasn't locker room banter. This was a powerful individual speaking freely and openly about sexually predatory behavior. And actually bragging about kissing and groping women," said Obama, 52.

"It doesn't matter what party you belong to... no woman deserves to be treated this way. No one deserves this kind of abuse," she said.

"This is not normal. It is not politics as usual. This is disgraceful. It is intolerable."

Speaking in deeply personal terms, Obama said the Trump scandal "has shaken me to my core."

The allegations against Trump suggest a decades-long pattern of sexually inappropriate behavior.

Jessica Leeds, a 74-year-old former businesswoman, told the Times that Trump groped her on a flight in the early 1980s, grabbing her breasts and reaching up her skirt.

"He was like an octopus," Leeds said.

"His hands were everywhere," she added. "It was an assault."

Accuser Rachel Crooks said she was a 22-year-old receptionist at a real estate company in Trump Tower in 2005 when she encountered Trump outside an elevator.

After she introduced herself, he "kissed me directly on the mouth," she told the Times.

- 'Against the wall' -
A photographer's assistant alleged that Trump grabbed her rear end at his Mar-a-Lago estate in Florida in 2003, while a former staff writer for People accused Trump of forcibly kissing her during an interview there in 2005.

"Trump shut the door behind us," Natasha Stoynoff wrote. "I turned around, and within seconds he was pushing me against the wall and forcing his tongue down my throat."

Trump dismissed the Stoynoff account out of hand.

"Look at her. Look at her words," he said. "You tell me what you think. I don't think so."

Two beauty pageant contestants also accused Trump of either groping or forcibly kissing them.

Trump rejected the claims again at a speech to young voters in Columbus, Ohio.

"I never met these people. I don't even know who they are. They're made-up stories filed right before the election," he said. "I wonder if that had anything to do with this."

With the campaign mudslinging in full force, Trump had repeatedly threatened to damage Clinton by reviving allegations of sexual misconduct by her husband.

He made good on that promise by appearing with three of Bill Clinton's female accusers ahead of Sunday's debate, and alleging on stage that the former president was "abusive."

He also turned deeply sinister Thursday, charging that Clinton met "in secret with international banks to plot the destruction of US sovereignty in order to enrich these global financial powers."

Clinton, visiting a campaign field office in San Francisco, briefly addressed the ugliness of the presidential race.

"We cannot let this pessimism, this dark and divisive and dangerous vision of America, take hold in anybody's heart," she said, adding that he has attacked more than just women.

"There's hardly any part of America that he's not targeted."