A leading human rights lawyer has been sentenced to four and a half years in prison for defending cases that were seen as sensitive by the Chinese government.

Wang Quanzhang was arrested in 2015 as part of a crackdown in which more than 200 activists and rights workers were detained by the authorities.

Human Rights Watch said Mr Wang’s lengthy sentence - on a charge of subversion of state power - made a “mockery” of the rule of law President Xi Jinping claimed to uphold. Amnesty International's China researcher Doriane Lau called it a “gross injustice”.

“It's outrageous that Wang Quanzhang is being punished for peacefully standing up for human rights in China. He must be immediately and unconditionally released,” she said.

Mr Wang was held for more than three years before he was tried in a closed hearing on 26 December that lasted just one day. Foreign journalists and diplomats were barred from attending.

On Monday morning, the court in the north-eastern city of Tianjin announced the sentencing in a statement online. Mr Wang was “found guilty of subverting state power, sentenced to four years and six months in prison, and deprived of political rights for five years”, the statement read.

The charge of subversion is loosely defined in Chinese law and it wasn't clear what specific illegal acts Mr Wang had been accused of committing.

The lawyer had sought to use the letter of Chinese law to defend citizens against the state - pursuing land rights cases on behalf of poor villagers, accusations of police torture or defending members of the banned Falun Gong spiritual movement.

Such was the secrecy surrounding his own detention that many, including his wife Li Wenzu, did not know for a long time whether or not he was alive. She was barred from attending the December hearing by security forces.

Ms Li has championed her husband's case since he went missing, staging a 100 km (62 miles) march from Beijing to Tianjin, shaving her head to protest his treatment and filing almost weekly petitions to the Supreme People's Court.

Li Wenzu has her head shaved to protest the detention of her husband and Chinese human rights lawyer Wang Quanzhang (AFP/Getty Images)

She wrote in a statement on Twitter that her husband was innocent and the "inhuman" behaviour of law enforcement officials toward Wang was a violation of Chinese law.

"I respect and support every choice that Wang Quanzhang has made. I will continue to defend Wang Quanzhang's rights," she said.

The UN has previously raised Mr Wang’s case, calling on authorities to "ensure his due process rights are respected” after the December hearing, and saying there were "serious human rights concerns" about the way his case had been handled.

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The 2015 crackdown on rights lawyers was seen as a major turning point in President Xi’s rule, showing a ruthless streak as he crushed any potential challenge to his authority.