A leading Hong Kong university has taken down a statue from its campus site that for more than two decades has commemorated pro-democracy protesters killed during China's Tiananmen Square crackdown in 1989, Reuters witnesses said.

Late on Wednesday night, security guards at the University of Hong Kong (HKU) placed yellow barricades around the eight-meter (26-foot) high, two-ton copper sculpture called the "Pillar of Shame" that commemorates those killed by Chinese authorities more than three decades ago.

The artwork, of anguished human torsoes, is one of the few remaining public memorials in the former British colony to remember the bloody crackdown that is a taboo topic in mainland China, where it cannot be publicly commemorated.