A prestigious public university in Mexico was forced to cancel its entrance examination after nearly all candidates bagged perfect scores in an assessment known to be tough in the country.

Administrators of the National Autonomous University of Mexico, or UNAM, have annulled the exams after an unusually high number of candidates emerged successful, marking it as a first in the institution’s history.

The university announced that the exams would be re-administered at a yet-to-be announced date, fixing the start of classes for August 10.

Allegations of cheating with artificial intelligence swirled as candidates who typically struggle to pass the examination for admission to UNAM excelled brilliantly after results were released.

It was the first time the university administered the exams online, allowing candidates the liberty to take the assessment from the comfort of their homes using the Internet.

Earlier this week, UNAM’s president Leonardo Lomelí said the university was working to clarify what happened, stating an investigation was underway.

“The university must stand with those who studied, who prepared and who sought the entrance exams to access higher education,” said Mr Lomelí. “We are interested in clarifying what happened, in seeking the best way to guarantee equitable access for all applicants to the higher education provided by the university.”

At least 40,000 candidates are again expected to sit for the exams to compete for the 20,000 available spots.

Mr Lomelí apologised to students who studied hard for the cancelled exams, explaining that the annulment was necessary.