TAIPEI (AFP) - The wife of a Taiwanese democracy activist jailed in China flew to the country on Monday (March 26) after being granted permission to visit him in prison for the first time, in a case that has strained cross-strait relations.

NGO worker Lee Ming Cheh was sentenced to five years in prison in November on charges of subverting state power by a court in central Hunan province, as activists face increased pressure from authorities under Chinese President Xi Jinping.

Taipei has called Lee's jailing "unacceptable" and a serious blow to relations, while his wife Lee Ching Yu has said his trial was a "political show".

She told reporters prior to her departure on Monday that she intends to pass on "messages from the free world" during her planned visit to see him in prison on Tuesday.

Lee was arrested in March 2017 during a trip to the mainland and held incommunicado for months.

Chinese authorities cancelled Ms Lee Ching Yu's mainland travel permit last April as she searched for her missing husband and later only granted her single-entry visas to attend the trial and sentencing.

But in January, she was barred from boarding a flight to visit Lee in Hunan's Chishan prison.

During his trial, Lee admitted the charges, stating that he had written and distributed online articles that criticised China's ruling Communist Party and promoted democracy.

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

Amnesty International and Taiwanese rights groups have vowed to continue pushing for Lee's release.