More Americans now hold an unfavorable view of the leading Democratic US presidential candidate, Hillary Clinton, as well as her Republican rivals, according to a new poll.

Just 39 percent of Americans have a favorable view of Clinton, while 49 percent have an unfavorable view, an Associated Press-GfK poll has found.

The poll shows that negative ratings of Clinton have increased over the past few months, especially among Democrats.

In an AP-GfK survey taken at the end of April, 46 percent had a favorable opinion and 41 percent had an unfavorable opinion of the former secretary of state, senator and first lady.

Perhaps most concerning for Clinton, according to the July survey, is that only 4 in 10 voters view her as a "compassionate” person towards average Americans and just 3 in 10 think she is an "honest" individual.

"I used to like her, but I don't trust her," said Donald Walters of Louisville, Kentucky, who participated in the poll. "Ever since she's announced her candidacy for the presidency I just haven't liked the way she's handled things. She doesn't answer questions directly."

"I don't think she comes across very genuine,” said Stephanie Bergholdo, a Democratic voter from Oak Park, California. “She just seems a little stiff to me.”

Clinton, however, isn't the only candidate with negative ratings.

Nearly all of the Republican candidates for president are viewed more negatively than positively, some of them by large margins, the poll shows, and many of them are unfamiliar to large swathes of Americans.

Least popular of all is billionaire investor Donald Trump, viewed unfavorably by 58 percent of Americans and favorably by just 28 percent.

The poll also shows that negative views of GOP presidential hopeful former Florida governor Jeb Bush are on the rise, at 44 percent, up from 36 percent in April.