The US Supreme Court on Thursday struck down race-conscious admissions programs at Harvard University and the University of North Carolina, effectively prohibiting affirmative action policies long used to raise the number of Black, Hispanic and other underrepresented minority students on American campuses.

In a blockbuster decision that will force many colleges and universities to overhaul their admissions policies, the justices ruled that affirmative action admissions programmes that consider an applicant's race in ways like Harvard and UNC did violate the US Constitution's promise of equal protection under the law.

Powered by the conservative justices with the liberals in dissent, the court ruled in favour of a group called Students for Fair Admissions, founded by anti-affirmative action activist Edward Blum, in its appeal of lower court rulings upholding programs used at the two prestigious schools to foster a diverse student population. The vote counts were 6-3 against UNC and 6-2 against Harvard.

In major rulings last year with far-reaching societal implications also spearheaded by the conservatives justices, the court overturned the 1973 Roe v. Wade decision that had legalised abortion nationwide and widened gun rights in a pair of landmark rulings.

Speaking at the White House, Democratic President Joe Biden said he strongly disagreed with Thursday's ruling, written by Chief Justice John Roberts, and urged colleges not to abandon their commitment to having diverse student enrolment. Asked by a reporter if this is "a rogue court," Biden replied, "This is not a normal court."

Roberts wrote that a student "must be treated based on his or her experiences as an individual not on the basis of race. Many universities have for too long done just the opposite. And in doing so, they have concluded, wrongly, that the touchstone of an individual's identity is not challenges bested, skills built, or lessons learned but the colour of their skin. Our constitutional history does not tolerate that choice."

According to Harvard, around 40 percent of US colleges and universities consider race in some fashion. Blum's group in lawsuits filed in 2014 accused UNC of discriminating against white and Asian American applicants and Harvard of bias against Asian American applicants.

Harvard and UNC have said they use race as only one factor in a host of individualised evaluations for admission without quotas - permissible under previous Supreme Court precedents - and that curbing its consideration would cause a significant drop in enrolment of students from under-represented groups.

Affirmative action had withstood Supreme Court scrutiny for decades, most recently in a 2016 ruling involving a white student, backed by Blum, who sued the University of Texas after being rejected for admission.

The Supreme Court has shifted rightward since 2016 and now includes three justices who dissented in the University of Texas case and three appointees by Republican former President Donald Trump, who is running again in 2024. Trump on Thursday hailed the ruling as "a great day for America." (Reuters)