HONG KONG - Thomas and Raymond Kwok, the billionaire co-chairmen of Sun Hung Kai Properties, and Rafael Hui, the former head of Hong Kong's civil service, were charged Friday in a bribery investigation surrounding Asia's largest developer, the city's official broadcaster reported.

Two others have also been charged in the case, which alleges offences linked to bribery and misconduct in public office. They include Thomas Chan, the board member in charge of land purchases at Sun Hung Kai Properties, and Francis Kwan, a former banker, according to Hong Kong's RTHK.

Kwan is a friend of Hui's, sources have told Reuters, and investigators have been looking into payments between Chan, Kwan and Hui. The five men were charged by Hong Kong's anti-corruption agency, RTHK reported.

The men had returned to the Independent Commission Against Corruption (ICAC) anti-graft body on Friday, according to Reuters reporters at the scene, but left after a brief visit. Their appearance comes almost four months after the first arrests in the highest profile case in the agency's history.

Chan, the company's board member in charge of land purchases and the first man arrested in the case, also appeared at the agency.

"I'm just shocked and horrified like everybody else," Roger Nissim, the former manager of the company's project planning department, said. "It's the last company anybody would have expected to have this happen. The overriding feeling is that it's sad that it's come to this."

The Kwoks were accompanied by their legal team, Reuters reporters outside the headquarters of the ICAC said. The agency has been investigating alleged corruption and misconduct in public office.

Walter Kwok, ousted as chairman of Sun Hung Kai Properties and estranged from his brothers, was also arrested at the end of May.