A leading law professor has been barred from taking up a senior post at one of Hong Kong's top universities in what some said was a blow to academic freedom as Beijing tries to tighten its grip a year after student-led protests rocked the city.

For more than a century, HKU, one of Asia's top universities, has served as a bastion of liberal education in the city that returned from British to Chinese rule in 1997, producing many of its top politicians, bureaucrats and lawyers.

Hong Kong's constitution guarantees the financial enclave a high degree of autonomy denied in mainland China by its Communist leaders, including academic freedom, broad individual rights and an independent judiciary.

But the university's governing council, stacked with supporters of the Beijing-backed Hong Kong government, has thwarted the appointment of former HKU law school dean Johannes Chan as a university pro-vice-chancellor.

He had been recommended for the post last year by a university search committee headed by HKU's president after a global recruiting drive.

Liberals see Professor Chan's blocked appointment as part of a broad move to limit academic freedom at an institution whose students and academics played a big role in 79 days of protests last year that saw thousands take to the streets demanding full democracy.

"It's obvious that the decision was a political one," said Ip Kin-yuen, a lawmaker and head of an HKU alumni association that recently saw 7,800 of its members voice support for Chan.

"Academic freedom will no longer exist after this."

Some students held a candlelight vigil in support of Professor Chan while the student union said they'd consider further protests.