BEIJING -- More than 54,000 Chinese officials were investigated by prosecutors for bribery, dereliction of duty and other duty-related crimes in 2015, anti-graft chief Wang Qishan said in a work report published on Sunday.

More than 20,000 cases were concluded by courts nationwide, including 16,000 cases involving bribery and embezzlement, and 4,300 cases of dereliction of duty, according to the work report made by Wang, chief of the Communist Party of China's Central Commission for Discipline Inspection (CCDI), at the sixth plenary session of the 18th CPC CCDI on Jan. 12.

Tallying up anti-corruption efforts in the past year, Wang said disciplinary authorities received more than 2.8 million tip-offs, and punished about 336,000 discipline violators in 2015.

Investigations into 90 centrally-administered officials for discipline violations were launched or finished in 2015, said the report, adding 42 of them have been transferred to judicial organs for criminal investigation.

Graft busters also probed 49,000 officials for suspected violation of the eight point anti-extravagance rules, 34,00 of them were published according to the disciplinary rules.

The discipline inspection agencies have been firm in dealing with its corrupt elements. A total of 2,479 discipline inspectors nationwide were punished in 2015, according to the report.

An initiative called "Sky Net" unveiled by Chinese government saw 1,023 fugitives being returned from overseas in 2015, recovering 3 billion yuan ($461.5 million) in criminal proceeds.