Former US Secretary of State Hillary Clinton has compared US President Donald Trump's "imperiled presidency" to that of Richard Nixon's in a fiery commencement speech at her alma mater Wellesley College.

"We were furious about the past presidential election of a man whose presidency would eventually end in disgrace with his impeachment after firing the person running the investigation into him at the Department of Justice," Clinton said, before clarifying she was speaking about Nixon.

In 1973, President Nixon ordered the then Attorney General to fire a special prosecutor who was looking into taped conversations recorded in the Oval Office as part of the Watergate scandal. He later resigned while facing the threat of impeachment in 1974. 

Clinton's reference to Nixon's firing of an investigator, in a graduation speech at the college on Friday, was an apparent knock at Trump's controversial decision to sack his former FBI Director James Comey, CNN reported. 

Since Comey's ouster, the President has been accused of urging Comey to end a probe into his ex-National Security Adviser Michael Flynn.

She took repeated veiled shots at Trump for having launched "a full-fledged assault on truth and reason" and proposing a budget that represented an "attack of unimaginable cruelty on the most vulnerable among us".

Her sharp remarks met thunderous applause and cheers from the graduating class. She went on to say that "when people in power invent their own facts and attack those who question them, it can mark the beginning of the end of a free society".

Wellesley College president Paula Johnson noted in her introduction of Clinton that the famous alum almost broke the "highest, hardest glass ceiling."

"And she won the popular vote," Johnson added.

Clinton herself joked that she got through the aftermath of the election with the help of friends, family and wine.

"Long walks in the woods. Organising my closets," she said. "Chardonnay helped a little too."

The former presidential nominee's commencement speech came more than six months after her defeat to Trump, and almost five decades after a young Hillary Rodham's speech at her own graduation thrust her into the national spotlight, according to the report.

Following the speech, Republican National Committee chairwoman Ronna McDaniel said that Clinton's comments were a "stark reminder why (she) lost in 2016" and accused her of "lashing out with the same partisan talking points".