“It’s not hard to find a small handful of people willing to make false smears,” he told a rally on Friday.
Two new accusations came from an ex-Apprentice contestant who cited a 2007 incident and a woman who described a case from the early 1990s.
Polls suggest Mr Trump is losing ground in some of the key battleground states.
During the rally in North Carolina, the Republican candidate said the accusations were “sick” and false, and driven by fame, money or politics.
“Or for the simple reason they want to stop our movement, they want to stop our campaign. Very simple,” he told the crowd.
He added: “These claims defy reason, truth, logic, common sense. They are made without supporting witnesses.
“When the media does what they’re doing now, that’s rigging the system… The election is rigged.”
Saying he was ignoring his own advisers by commenting on the allegations, he suggested that he would never have been attracted to Jessica Leeds, one of this accusers.
“Believe me, she would not be my first choice, that I can tell you.”
One of the new allegations involves Kristin Anderson, who told the Washington Post the property mogul touched her through her underwear at a Manhattan nightspot in the 1990s.
Ms Anderson, now 46, said she was “very grossed out and weirded out”.
She added: “It wasn’t a sexual come-on. I don’t know why he did it. It was like just to prove that he could do it, and nothing would happen.
The newspaper said it had approached Ms Anderson after learning of her story through a third party, and she had spent several days deciding whether to go public.
Mr Trump’s spokeswoman, Hope Hicks, said in a statement emailed to the Washington Post: “Mr Trump strongly denies this phony allegation by someone looking to get some free publicity. It is totally ridiculous.”
Meanwhile, Summer Zervos, who was a contestant on season five of The Apprentice in 2006, said the businessman forced himself on her at a Los Angeles hotel and began “thrusting his genitals”.
She had been invited by him to discuss job opportunities.
Ms Zervos, 41, told an emotional news conference in Los Angeles that she met him in 2007 in a bungalow at the Beverly Hills Hotel, where the businessman greeted her by kissing her on the mouth.
She said he asked her to sit next to him on a sofa where he “grabbed my shoulder and began kissing me again very aggressively and placed his hand on my breast”.
Ms Zervos fought back tears as she said Mr Trump attempted to lead her into the bedroom and “began thrusting his genitals”, even as she fended off his advances.
She was flanked during the press conference by well-known lawyer Gloria Allred, who has previously represented alleged sexual assault victims of entertainer Bill Cosby.
At the time of the alleged assault, Mr Trump was newly married to his third and current wife, Melania Trump.
He rebutted the suggestion on national television as he was asked about a leaked recording from 2005 in which he is heard bragging that he can force himself on women because he is a star.
Meanwhile, his campaign presented a British man who disputed the account of Ms Leeds, now 74. She alleged that when she was 38, Mr Trump groped her on a flight to New York, acting “like an octopus”.
The New York Post reported that Anthony Gilberthorpe contacted Mr Trump’s campaign to counter the claim. In an interview with the paper he said: “I was there, I was in a position to know that what she said was wrong, wrong, wrong.”
Mr Gilberthorpe made headlines in 2014 when he alleged that he had provided underage boys to British politicians for sex parties.