HONG KONG — Hong Kong’s anti-graft agency on Thursday arrested two billionaire brothers who run the biggest real estate company in the city, accusing them of suspected corruption.


The brothers, Raymond and Thomas Kwok, the joint chairmen of Sun Hung Kai Properties, were arrested by the Independent Commission Against Corruption in connection with an investigation into suspected bribery offenses, the company said in a regulatory filing to the Hong Kong stock exchange on Thursday.


The firm said the I.C.A.C issued a search warrant for its offices and it had “been required to provide certain information with regard to the allegations.”


The “arrests have not affected and will not affect the normal business and operations of the Group,” Sun Hung Kai said in the filing.


The I.C.A.C. confirmed earlier on Thursday that it arrested two unidentified senior executives of a listed company and an unidentified former principal official of the Hong Kong government for alleged violations of anti-bribery laws.


The South China Morning Post, a Hong Kong newspaper, identified the government official as Rafael Hui, the former chief secretary of the civil service, the second-highest position in the local government. Mr. Hui resigned Thursday from his role as an independent director of A.I.A., the Asian arm of the American insurance giant A.I.G. Group, “In order to attend to other commitments,” the company said in a stock exchange announcement.


The arrests sent shockwaves through Hong Kong, a city traditionally known for cosseting real estate tycoons, not arresting them.


The Kwok brothers control a family fortune worth $18.3 billion as estimated by Forbes, which earlier this month ranked them as No. 27 on a list of the world’s billionaires.


“They have so much money, they can buy anything,” said Francis Lun, a managing director at the Hong Kong brokerage Lyncean Holdings.


But growing discontent in Hong Kong with the city’s widening wealth gap and a lack of ballot-box democracy have in recent years heightened criticisms against what is often viewed as collusion between government officials and property developers.