Donald Trump belittled the physical appearance of Carly Fiorina, his fellow Republican US presidential candidate, in remarks published on Wednesday, saying: "Look at that face. Would anyone vote for that?"
The comments by the billionaire real estate developer, published in an article on the website of 'Rolling Stone' magazine, were aimed at the only woman in the large field of Republicans vying for their party's 2016 presidential nomination.
The magazine reported that Mr Trump, who is leading his Republican contenders in the polls, made the remarks while watching Ms Fiorina, the former Hewlett-Packard Co chief executive, on television.
"Can you imagine that, the face of our next president?" he is quoted as saying. "I mean, she's a woman and I'm not supposed to say bad things, but really, folks, come on. Are we serious?"
Ms Fiorina, in an interview on Fox News Channel, said she viewed the remarks as "very serious".
"Maybe, just maybe, I'm getting under his skin a little bit because I am climbing in the polls," she said.
Mr Trump's remarks were his latest barbs aimed at a woman during the campaign.
Last month, he criticised Megyn Kelly, Fox News Channel anchor, during and after a Republican debate.
During the debate, Ms Kelly had asked Mr Trump about comments referring to women as "fat pigs" and slobs. Asked about Ms Kelly in a CNN interview last month, Trump said: "You could see there was blood coming out of her eyes. Blood coming out of her wherever."
And it was not the first time he has taunted Ms Fiorina.
A month ago he tweeted: "I just realised that if you listen to Carly Fiorina for more than 10 minutes straight, you develop a massive headache. She has zero chance."