BEIJING, July 3 (AFP) — China appointed a hardliner involved in a clamp down against protests on the mainland as the head of Hong Kong's new security agency on Friday, state media said, days after imposing a sweeping law on the territory that criminalises dissent.

Zheng Yanxiong will take the helm of the controversial national security agency, a new office set up under the legislation that empowers mainland security agents to operate inside Hong Kong openly for the first time, unbound by the city's laws.

The office — which has investigative and prosecutory powers — will monitor intelligence related to national security and process cases, in some circumstances handing them over to the mainland for trial, according to the law.

Zheng rose through the ranks of the local government in southern Guangdong province which borders Hong Kong, to serve as secretary general of the provincial Communist Party committee.

The 56-year-old is known as a hardliner who stamped out often-violent anti-corruption protests that erupted in Wukan, a village in the province, in 2011 after a local activist died in police custody.

"He is a tough enforcer, a law and order person," Willy Lam, an expert on China's Communist Party at the Chinese University of Hong Kong, told AFP. 

Lam said Zheng could speak Cantonese, Hong Kong's lingua franca, unlike other recent appointments of senior party officials who deal with Hong Kong. 

"His experience in cracking down on riots in Guangdong will endear him to the authorities," he added.

During the Wukan riots, multiple Hong Kong media outlets quoted Zheng as saying villagers were "colluding with foreign media to create trouble".

Hong Kong was rocked by several months of huge and sometimes violent pro-democracy protests last year, a movement which Beijing has vowed to end with its new security law.

China has dismissed protesters' demands for greater democracy and portrayed the unrest as a foreign plot to destabilise the motherland. 

On Friday, the State Council also named Luo Huining — the current director of Beijing's Liaison Office in the semi-autonomous city — as the national security adviser to the city's newly-formed national security commission chaired by Chief Executive Carrie Lam.

Luo was appointed to the Liaison Office in January despite reaching retirement age. A loyalist of president Xi Jinping, he built a reputation for enforcing Communist Party discipline and tackling corruption.

Another senior party leader involved in crackdowns on underground churches was appointed to lead the Hong Kong and Macau Affairs Office in Beijing. 

Hong Kong's mini-constitution forbids mainland officials from interfering in the running of Hong Kong's day-to-day affairs.

But Beijing has argued national security is purely the purview of central authorities.

While the new security agency in Hong Kong is entirely run by mainland personnel the national security commission contains a mixture of Hong Kong and mainland officials.

On Thursday the State Council appointed veteran Hong Kong official Eric Chan Kwok-ki as the commission's secretary general.

The commission — also created by the new law — will oversee policy formulation relating to the national security law in Hong Kong.