A video grab from footage on the website of Yueyang Intermediate People's Court shows activist Lee Ming-cheh, the first Taiwanese person to be convicted of subverting government power under China's criminal code

A Chinese court sentenced Taiwanese democracy activist Lee Ming-cheh to five years in prison on Tuesday on charges of attempting to subvert state power, further souring cross-strait ties.

Lee sat nervously as the three-judge panel read the sentence at the Yueyang intermediate people's court in central Hunan province, according to a video posted on the tribunal's social media account.

Taiwan and human rights groups immediately denounced the ruling as "unacceptable" and "politically motivated".

Lee -- an NGO worker who was arrested during a trip to the Chinese mainland in March -- is the first Taiwanese person to be convicted in China on the political charge, according to Taiwan's Judicial Reform Foundation.

A Chinese co-defendant named Peng Yuhua was sentenced to seven years in prison.

The court said both men stated that they would not appeal their sentences.

President Xi Jinping, who consolidated power at a Communist Party congress last month, has cracked down on dissent and tightened control on civil society since taking office in 2012.

Lee had confessed to the charges during his trial in September, stating that he had written and distributed online articles that criticised China's ruling Communist Party and promoted democracy among other topics.

His wife, Lee Ching-yu, who attended the sentencing, said her husband had "paid the price" for his ideals.

"Fighting for human rights for the disadvantaged is a commitment that must be made to push for the enhancement of human civilisation... I want to express again that I am proud of his dedication," she said in a statement.

Amnesty International East Asia research director Roseann Rife called for Lee to be "immediately and unconditionally released", saying he had committed no crime.

"Lee Ming-cheh is the victim of a politically motivated prosecution... He is the latest to suffer under the Chinese authorities' relentless attack against human rights and democracy activists," Rife said.

Taiwan's presidential office and the ruling Democratic Progressive Party (DPP) called the verdict "unacceptable".

"We urged the Beijing authorities to release Lee and allow him to return to Taiwan soon. We regret that Lee's case seriously damaged cross-strait relations," the presidential office said in a statement.

China sees self-ruled Taiwan as part of its territory waiting to be reunified.

- 'Political show' -

Former DPP lawmaker Wang Li-ping tried to go to the court with Lee's wife, but Wang was expelled from mainland China upon arrival at Changsha airport.

Lee has long supported civil society organisations and activists in China, according to Amnesty International, and was said to have frequently travelled between the mainland and Taiwan.

He had shared "Taiwan's democratic experiences" with his Chinese friends online for many years and often mailed books to them, said the Taiwan Association for Human Rights.

After Lee went missing, Chinese authorities confirmed he was being investigated for suspected activities "endangering national security".

In the lead-up to the trial, Beijing repeatedly ignored Taipei's requests for information on Lee's whereabouts and details of the allegations against him.

His wife had called his trial a "political show".

When he pleaded guilty in September, Lee told the court: "I know that my behaviour definitely violated Chinese law".

Lee's wife, a friend and two officials from Taiwan's semi-official Strait Exchange Foundation were allowed in.

"A Taiwanese who has valid documents and the reason for her visit to China is clear, it's just to accompany the family of a man on trial and to stay for two nights with return ticket already booked but she can be expelled anytime for no reason? I am speechless," Lee Ching-yu said in an earlier statement.

Relations between Beijing and Taipei have worsened since Taiwanese President Tsai Ing-wen took office in May last year, with China cutting off all official communications with the island.

Beijing wants Tsai to acknowledge the island is part of "One China", which she has refused to do.