HONG KONG—In a case that strikes at the heart of Hong Kong’s business and political elite, two real-estate tycoon brothers and the city's former No. 2 official were arrested on suspicion of bribery.

Thomas Kwok, 60 years old, and Raymond Kwok, 58, were arrested Thursday by Hong Kong's antigraft agency, said Sun Hung Kai in a statement late in the day. The Kwok brothers and their families control Sun Hung Kai, one of the world's biggest real-estate developers, which built some of the most famous towers in Hong Kong’s skyline.

The arrest of the Kowk brothers is a blow to the exclusive club of businessmen and politicians that has ruled Hong Kong since before Britain handed over the city to China in 1997.

A small group of powerful organizations control real estate, transportation and communications in Hong Kong, and the spectacle of the two tycoons walking into law-enforcement offices to answer questions in a bribery case riveted the city’s inhabitants.

"It's been a long time since such senior figures in the construction industry have been subject to such attention," said Steve Vickers, chief executive at Steve Vickers & Associates, a Hong Kong risk consultancy.

The Independent Commission Against Corruption also arrested the city's former No. 2 official, Rafael Hui, also on suspicion of bribery and on suspicion of misconduct in public office, a person familiar with the situation said. Sun Hung Kai said the Independent Commission Against Corruption searched the company's offices on Thursday.

The Kwok brothers couldn't be reached, and the names of their lawyers couldn't be learned. Attempts to reach Mr. Hui or his office were unsuccessful.