The admittance of Australia's ambassador to China to a tightly guarded Beijing court where the espionage case against Australian blogger Yang Hengjun will be heard on Thursday has been denied.

In accordance with a two-way consular deal, Graham Fletcher attempted to enter Beijing's No. 2 Intermediate People's Court.

“Unfortunately, we have merely turned away from the court. The explanation provided was due to the pandemic situation, but the Foreign Ministry also informed us that it is a national security case, therefore we are not able to attend,” Fletcher said outside the court.

“This is quite regretful, alarming, and disappointing. We have long had concerns about this case, including a lack of openness, and have decided that it is an example of arbitrary detention.”

The case is steeped in secrecy, with no information about the espionage agency for which Yang is believed to have work published. Yang faces a maximum sentence of ten years in prison if convicted of harming national security.

Marise Payne, Australia's foreign minister, had previously expressed her displeasure with Yang's treatment, expressing concerns about "procedural fairness." Payne's remarks were deemed "deplorable" by the Chinese embassy in Australia.

According to a bilateral treaty on consular contacts, Payne had asked China to allow Australian diplomats to attend the trial. The one-day trials of Canadians Michael Kovrig and Michael Spavor were held in secret in China earlier this year. At the time, the courts stated that they involved state secrets.

Joshua Rosenzweig, the head of Amnesty International's China team, said in a statement this week that Yang's allegations "appear to be a politically motivated prosecution for the article."