US Democratic presidential frontrunner Hillary Clinton has ripped into Republican rival Donald Trump, bashing the New York billionaire as a “loose cannon” who is risky for president.

"He (Trump) is a loose cannon, and loose cannons tend to misfire," Clinton told CNN on Wednesday, a day after the business mogul emerged as the presumptive presidential nominee for the Republican party.

The former secretary of state stressed that Trump should offer policy specifics before the presidential election, criticizing him on certain issues such as abortion, nuclear weapons and climate change.

"He makes these grand statements and grand accusations. At some point when you're running for president, you actually have to put a little meat on the bones. You've got to tell people what it is you're going to do and how you're going to do it,” she added.

On Tuesday, Clinton lost to her rival Bernie Sanders in Indiana’s crucial primary. She, however, is anticipated to win Democratic party’s nomination as she is leading Sanders by over 800 delegates.

Asked about the possibility of running against Trump in November's election, Clinton said, "This is to me a classic case of a blustering, bullying guy who has knocked out of the way all the Republicans because they were just dumbfounded."

Clinton added that she knew how to run against Trump and criticized the other Republican hopefuls who began the presidential campaign along with Trump.

"They didn't know how to deal with him. They couldn't take him on the issues because they basically agreed with them. And they didn't know how to counterpunch," she added.

Trump became the presumptive Republican nominee with 53.2 percent support, followed by Ted Cruz with 36.7 percent and John Kasich with only 7.6 percent.

Cruz and Kasich later officially suspended their presidential campaigns following their failure in the Indiana primary.