A woman has made sexual harassment allegations against Republican US presidential hopeful Herman Cain, telling a news conference that he attempted to inappropriately touch her in 1997.

Sharon Bialek told reporters in New York on Monday that she met with Cain to ask about getting her old job back at the National Restaurant Association when the incident happened in Washington.

At the time, Cain was chief of a restaurant trade group. Bialek said Cain reached under her skirt and reached for her genitals after she had asked for his help.

She is among three others who have made sexual allegations against Cain, but the only to have gone public with the accusation, while the others remained anonymous.

Cain has denied all the allegations and called "completely false".

Alan Fisher reports from Washington.