Hillary Clinton and Bernie Sanders blasted each other in the most heated debate of their campaigns as the two continued to battle for important New York votes in the upcoming primary. Sanders lashed out at Clinton's "lack of judgment" while Clinton attacked Sanders' support for guns and his policies.

Clinton found herself briefly on the ropes again over her paid speeches to big banks and said she would not release the transcripts when pressed by CNN moderators during the debate.

Sanders was also asked to name a single policy decision Clinton made as senator that showed she was under the thumb of the banks. He said that when the "greed and recklessness of Wall Street" led to the financial crisis, he had called on the big banks to be broken up – while Clinton was "busy giving speeches to Goldman Sachs."

"He cannot come up with any example because there is no example," Clinton fired back.

She in turn criticised Sanders by noting his trouble explaining some of his core policies in a recent interview with the New York Daily News when he was unable to clearly describe how he would break up big banks. "Describing the problem is a lot easier than trying to solve it," said Clinton.

She also hit out at her political rival for his failure to release his tax returns so far. Sanders vowed to release his past returns on 15 April. The crowd in the debate spurred on the raucous conflict between the two by either cheering loudly or hissing.

Clinton's most powerful punch was against Sanders' weak stance on gun control. Sanders holds an unusual position on the issue for a liberal politician because the senator represents the largely rural state of Vermont including many hunters who generally oppose more gun controls. Clinton accused Sanders of having made a "commitment to the NRA" to oppose a waiting period for background checks on gun purchases.

Clinton also brought up a recent request from the daughter of the Sandy Hook Elementary School principal who was killed during the Newtown massacre, asking the senator to apologise to the victims for "putting the gun lobby above our families." Sanders dodged making an apology.

The back-and-forth exchanges became so intense that at one point, moderator Wolf Blitzer warned: "If you're both screaming at each other, the viewers won't be able to hear either of you."

One issue they united over was climate change, which they both called a worldwide crisis. But they differed on tactics. Sanders called again for sweeping steps: a tax on carbon-dioxide emissions and an end to fracking among other measures.

But Clinton said that Sanders' ideas were not politically or logistically feasible and that trying to implement them would waste time.

Polls show that Clinton is likely to defeat Sanders in New York. Even though she has a sizeable delegate lead over her Democrat rival, it is critical to her campaign that she wins the state.

Sanders has proven to be a surprisingly resilient candidate with steadfast support from liberals and younger voters. The New York primary comes after a string of victories for Sanders in Wyoming, Wisconsin, Idaho and Utah. If Sanders ekes out a victory in New York, it would be a serious blow to Clinton.