HONG KONG, Feb 28 -- Macau's anti-corruption agency has begun an investigation into a former senior figure in the public prosecutions office, an official and lawmakers said on Sunday, the most high-profile graft case in the world's largest gambling hub in a decade.

The Commission Against Corruption said in a statement on its website on Saturday that it had initiated a criminal investigation into a case involving "former leadership staff of the Public Prosecutions Office" (PPO) who received illicit gains of 44 million patacas from public work contracts worth more than 167 million patacas ($21 million).

Two lawmakers and several casino executives confirmed to Reuters that Ho Chio Meng, chief prosecutor until 2014, was the key official being investigated.

Ho, who was once tipped as a candidate for the chief executive post in the former Portuguese colony that reverted to Chinese rule in 1999, was photographed by Macau media entering the enclave's court of final appeal on Saturday.

"It is Ho," said one lawmaker, who asked not to be identified because of the sensitivity of the issue.

"I am not surprised as in 2015 he was not seen in Macau for many months and it was said that he was in the mainland."

The South China Morning Post reported that Ho had been arrested. It was not possible to reach Ho or any of his representatives for comment.

Macau's corruption body said some of the people involved in the corruption case had been detained, while travel restrictions had been put on others, as well as "suspension from public duties".

The investigation into Ho comes after nine people, including government officials, were investigated for graft in 2015. That was in stark contrast to 2014, when no high-profile officials were questioned about bribery.

Macau, the only place in China where nationals can legally gamble in casinos, has been trying to clean up its act after President Xi Jinping initiated a broad crackdown against corruption in 2014.

Former secretary for transport and public works, Ao Man-long, was arrested in 2006 for bribe-taking, money laundering and abuse of power. There had been no large-scale investigations into officials after Ao's case until the appointment of Commissioner Against Corruption Cheong Weng Chon, who was sworn in during a visit by Xi in December 2014.

The push to wipe out graft in the southern Chinese special administrative region comes as gambling revenues have slumped to five-year lows, hitting the revenues of casino titans Sands China, Wynn Macau, Galaxy Entertainment , SJM Holdings, MGM China and Melco Crown.

($1 = 7.9990 patacas)