Over 8,000 students of a private vocational college have been affected by a cyber attack, the privacy watchdog said on Friday.

The Hong Kong College of Technology said its information technology network and file server were hacked in February.

A ransomware group is believed to have got hold of 450GB of the college's data and the information was made public on the dark web on Tuesday.

"This is not an ordinary attack, but a highly targeted and unusual cyber attack. The Hong Kong College of Technology condemns any cyber crimes and deeply apologises for any inconvenience and troubles caused by the incident," a spokesperson said.

The college said it reported the breach to the police and the privacy commissioner's office, shut down the affected system, and launched a probe with the help of independent cyber security experts.

It added that it will provide credit monitoring and dark web monitoring services to those affected for half a year at no cost.

In response to media enquiries, the privacy commissioner's office said it was informed about the data breach on February 21.

The watchdog said about 8,100 students had been affected and information involved included names, identity card numbers, emails, telephone numbers and addresses.

The Education Bureau urged the college to comprehensively investigate the incident and to take appropriate measures to strengthen network security to prevent further similar attacks.

Police said they are investigating the matter but no arrests have been made so far.