HONG KONG - The arrest of two brothers from one of Hong Kong's most powerful families and a former top government official is a major test for the city's anti-corruption agency, which has scored most of its recent successes in fighting lower level and petty graft.

Raymond and Thomas Kwok, the billionaire co-chairmen of Asia's largest developer Sun Hung Kai Properties were arrested on Thursday - and later released on bail - in the highest profile investigation ever launched by Hong Kong's Independent Commission Against Corruption (ICAC).

The graft-busting agency, set up in 1974 when crime and police corruption was rampant in the then British colony, has investigated top cops, government officials and construction executives.

But in the last few years critics complain the commission has failed to successfully prosecute any high level cases involving Hong Kong's rich and powerful, or the burgeoning new class of mainland Chinese entrepreneurs.

"This is the sort of case that would bolster the ICAC's public profile and credibility," said a source familiar with the agency, who did not want to be identified because of the sensitivity of the case.

Details of the investigation remain unclear and none of the arrested men have as yet been charged with any offence.

The Hong Kong public has been increasingly aggrieved at the perceived cosy ties between government and big business, especially the city's property tycoons. The issue played out in last month's Hong Kong election, and some observers have interpreted the arrests as a first move in an attempt to rein in the power of the monied elite.