The United States and Britain have expressed concern over a trial of Hong Kong activists accused of smuggling themselves to Taiwan.
Twelve pro-democracy activists were detained by China's coast guard in August as they tried to enter Taiwan by boat. They were later charged with navigating in waters illegally.
Many of them were on bail after being arrested or indicted in connection with anti-government protests in Hong Kong.
One of them is a pro-democracy activist who was arrested on suspicion of violating the national security law for the territory.
A trial for 10 of them started on Monday in a court in the southern city of Shenzhen, neighboring Hong Kong.
Diplomats from Western countries and Hong Kong journalists visited the court, but were not allowed to observe the hearing.
The court said it heard opinions from the prosecutors and the defense, without revealing further details of the proceedings.
Ahead of the first trial, the US Embassy in Beijing released a statement calling for the activists to be released. The statement said their so-called "crime" was to flee tyranny.
British Foreign Secretary Dominic Raab said on Monday that the activists were given just three days' notice of their trial, and have not had access to lawyers of their choosing.
He urged China to conduct trials in a fair and transparent manner.