Saudi authorities have transferred the trial of activist Loujain al-Hathloul to a court dealing with terrorism-related cases, her family said Wednesday, reporting she was visibly weak after more than two years in jail.

Hathloul, 31, was arrested in May 2018 with about a dozen other women activists just weeks before the historic lifting of a decades-long ban on female drivers.

Hathloul was "shaking uncontrollably" when she appeared at Riyadh's criminal court, where she has been tried since March 2019 in closed-door sessions, her sister Lina Hathloul said.

The judge announced that Hathloul's case had been "transferred to the Specialised Criminal Court (or) the terrorism court," Lina wrote on Twitter. "She looked weak in court... her voice was faint and shaky."

Two Western diplomats told AFP they were denied entry to the courthouse under the pretext of coronavirus restrictions. Despite her frail health, the activist read out her four-page defence to the judge, her other sister Alia al-Hathloul said on Twitter.

Hathloul's siblings are based outside the kingdom, but some of her other family members were said to be present in court.Riyadh's Specialised Criminal Court was established in 2008 to handle terrorism-related cases but has been widely used to try political prisoners.

Earlier this year, Amnesty International said the secretive court was being used to silence critical voices, including clerics and rights activists, under the cover of fighting terrorism. "Saudi authorities could have decided to end the two-year nightmare for brave human rights defender Loujain al-Hathloud," Amnesty International's Lynn Maalouf said in a separate statement on Wednesday.

"Instead, in a disturbing move, they transferred her case to... an institution used to silence dissent and notorious for issuing lengthy prison sentences following seriously flawed trials."

There was no immediate comment on the development from authorities in Saudi Arabia, an absolute monarchy that has long faced international criticism for its human rights record. While some detained women activists have been provisionally released, Hathloul and others remain imprisoned on what rights groups describe as opaque charges that include contact with foreign media, diplomats and activist groups.

The pro-government Saudi media has branded Hathloul and others as "traitors", and her family alleges she experienced sexual harassment and torture in detention. The detention of women activists has cast a spotlight on the human rights record of the kingdom, which has also faced intense global criticism over the 2018 murder of journalist Jamal Khashoggi in its Istanbul consulate.

 Hathloul began a hunger strike in prison on October 26 to demand regular contact with her family, but she ended it two weeks later, her siblings said. "She was being woken up by the guards every two hours, day and night, as a brutal tactic to break her," Amnesty said on Twitter, citing the activist's family.