A Hong Kong activist who posted an identity card database online in protest at a proposed law that would restrict access to information on company directors has removed the file from his website.

Corporate governance activist David Webb said he decided to take down the database of over 1,100 names, including some of the city's leading tycoons, on Friday after authorities said they were investigating his activities.

Hong Kong's privacy watchdog, the Office of the Privacy Commissioner for Personal Data, said it was looking into a "possible personal data breach".

Webb, who compiled the database from publicly available information said he was astonished at the decision, in a message on his website (www.webb-site.com).

"Our first, internal reaction was -- are you serious? For information that anyone could legally have found online?"

"All of this aims to increase transparency and accountability, and to reduce corruption, corporate fraud, money-laundering, identity fraud and other activities which are facilitated by a lack of transparency," Webb said.

"This has been a dark day for transparency in Hong Kong."

The database contained the identity card numbers of the two sons of Asia's Richest man, Li Ka-shing, as well as billionaire Sun Hung Kai Properties chairman Thomas Kwok, who is involved in the city's biggest graft scandal.

Under the proposed privacy law, corporate directors could apply to have their residential addresses and full identity card or passport numbers removed from the territory's registry of companies.

Such details were used in recent investigative reports by the New York Times and Bloomberg that alleged that the families of Chinese Premier Wen Jiabao and president-in-waiting Xi Jinping had accumulated billions in hidden assets.

Nearly 1,800 reporters, students and journalism professors have urged the government to withdraw the bill, saying it would infringe on press freedom.

A large number of Chinese companies are listed in the city, a financial hub that acts as a gateway for international firms seeking to tap into the booming Chinese market.