Harvard students protested after the US government said it intends to cancel all remaining financial contracts with the university, President Donald Trump's latest attempt to force the prestigious institution to submit to unprecedented oversight.

Hundreds of students gathered to oppose Trump's widening offensive, including Tuesday's measures estimated to be worth US$100 million, against the university that has drawn his ire for refusing to give up control of curriculum, admissions and research.

"Trump = traitor" read one student placard, while the crowd chanted "who belongs in class today, let them stay" in reference to Harvard's international students whose status Trump has upended by summarily revoking the university's accreditation to the country's Student and Exchange Visitor programme.

A judge issued a restraining order pending a hearing on the matter scheduled for Thursday, the same day as the university's commencement graduation ceremony for which thousands of graduating students and their families had gathered in Cambridge, Massachusetts near Boston.

The White House, meanwhile, doubled down in its offensive, saying that instead of Harvard public money should go to vocational schools that train electricians and plumbers.

"The president is more interested in giving that taxpayer money to trade schools and programmes and state schools where they are promoting American values, but most importantly, educating the next generation based on skills that we need in our economy and our society," press secretary Karoline Leavitt said on Fox News Tuesday evening.

"We need more of those in our country, and less LGBTQ graduate majors from Harvard University."

Tuesday's protest unfolded as news helicopters hovered overhead and graduating students in academic attire and their guests ate finger food at a reception on the lawns of Harvard Square nearby.

"All my international friends and peers and professors and researchers are at risk and [are] threatened with being deported – or their option is to transfer" to another university, said Alice Goyer, who attended the protest wearing a black academic gown.

"As a US student, it's my responsibility to speak out for them."

One history of medicine student from Britain graduating this week who gave his name only as Jack said that the policies pursued by Trump would make US universities less attractive to international students, even if the courts overturn the most damaging measures.

"The cloud may pass, but the damage will be done," said Jack, whose parents had travelled from Britain for the graduation ceremony.

Foreign students "who are here don't know where they stand, those overseas don't know if they'll be able to get back in... I don't know if I'd pursue a PhD here, six years is a long time," he added.

Alumni plan to file a lawsuit against Trump on June 9, filmmaker Anurima Bhargava told a virtual meeting staged by Crimson Courage, a grassroots alumni group that held a mass webinar to raise awareness and a fighting fund from former students.

The cutting of contracts announced on Tuesday – estimated by US media to be worth US$100 million – would mark the slashing of business ties between the government and a university that is the country's oldest and a research powerhouse. (AFP)