US Senator Bernie Sanders of Vermont has taken the lead over longtime front-runner Hillary Clinton in the state of New Hampshire, site of the first US presidential primary elections of 2016, according to a new poll.

Sanders leads Clinton by 44-37 percent among the likely primary voters for the Democratic Party, according to the Franklin Pierce University/Boston Herald survey released Tuesday.

US Vice President Joe Biden, who is still deciding whether he will run for president, is third in the New Hampshire poll at 9 percent.

This marks the first time Sanders has taken a lead in any state or national poll over Clinton, a former secretary of state, senator and first lady.

The poll has surprised many political analysts as the latest sign of Clinton’s potential weaknesses as a presidential candidate.

"Clinton is in free fall,” said Greg Valliere, the chief political strategist at the Potomac Research Group. "So the speculation will intensify — starting today — that Joe Biden may have to save the party from a debacle."

Sanders’ emphasis on US income inequality and influence of corporate money on elections and government has helped the senator attract large crowds on the campaign trail.

“This country belongs to all of us and not a handful of billionaires,” Sanders told an estimated crowd of more than 27,000 earlier this week in Los Angeles. “We need a grassroots political revolution.”

Clinton continues to lead her rival Democrats by a significant margin nationally, but her popularity numbers are declining.

Forty-eight percent of likely voters view Clinton unfavorably, compared with 37 percent who have a positive view of her, according to the latest NBC News/Wall Street Journal poll released last week.

There is mounting pressure on the US Justice Department to open a criminal investigation against Clinton for mishandling sensitive government information through her private server while she was secretary of state from 2009 to 2013.

She has come under intense criticism for using the personal email account for government business, potentially shielding her correspondence from public inquiries.