China's powerful former security chief Zhou Yongkang moved one step closer to trial Wednesday as authorities announced his case had been sent to prosecutors, amid a much-touted anti-graft sweep.

Zhou, whose arrest and expulsion from the ruling party last month sent shock waves through the Communist elite, is the highest-ranking figure to become ensnared in Chinese President Xi Jinping's campaign against corruption.

In a notice posted on its website, the Central Commission for Discipline Inspection (CCDI), the party's internal watchdog, said that the cases of Zhou and several other former top officials "have been transferred to judicial organs in accordance with the law".

"We will keep up the pressure in fighting corruption," it quoted supervision minister and CCDI deputy head Huang Shuxian as saying.

Others whose cases have been sent to the judiciary include former vice minister of public security Li Dongsheng; former top regulator of state-owned enterprises Jiang Jiemin, and former Sichuan province Political Consultative Conference chairman Li Chongxi.

All three have close ties to Zhou.

A fourth official, the former party chief of the China Association for Science and Technology Shen Weichen, has also had his case sent to prosecutors, the CCDI said.

Zhou was a close ally of disgraced politician Bo Xilai, whose hard-charging approach led to his ouster from the party's top ranks -- a factor that experts say contributed to Zhou's downfall.

After months of rumours, party authorities announced last July they were investigating Zhou, who retired from China's all-powerful Politburo Standing Committee in 2012.

Then, in December, he was arrested, ousted from the party and placed under a judicial probe on a barrage of charges including bribe taking and "leaking state secrets".

The state secrets charge makes it unlikely that Zhou's trial will be open to the public, according to analysts.

Days after his arrest, the Communist Party's flagship People's Daily newspaper branded Zhou a "traitor" and likened him to several past turncoats who were all executed.

The case makes Zhou the most senior party official to face prosecution since the 1980s and is part of Xi's wide-ranging anti-corruption drive that has vowed to take down both high-level "tigers" as well as low-level "flies".

But analysts say China has failed to implement institutional safeguards against graft, such as an independent judiciary and free media, leaving anti-corruption campaigns subject to the influence of politics.