The trial for Michael Kovrig, the Canadian detained more than two years ago in China on espionage charges, started yesterday, with relations between Ottawa and Beijing in free-fall.

The hearing comes days after the closed-door trial of another Canadian man, with both detained in apparent retaliation for Canada's arrest on a US extradition warrant of Huawei executive Meng Wanzhou.

Yester,day police cordoned off an area outside the Beijing court as Canadian diplomats were denied entry and turned away.

Kovrig, a former diplomat, was detained in 2018 and formally charged last June with spying at the same time as his compatriot, businessman Michael Spavor.

Jim Nickel, the charge d'affaires of the Canadian embassy in Beijing, told reporters that the hearing had started and that access for diplomats "has been denied."

"We're very troubled by the lack of access and lack of transparency in the legal process," he said.

A court official told reporters no entry was allowed because the trial is a national security case.

Representatives of 26 countries had gathered outside the building yesterday, Nickel said, and were "lending their voice" for Kovrig's immediate release.

The US is "deeply concerned at the lack of minimum procedural protections granted the two Canadian citizens", William Klein, Acting Deputy Chief of Mission of the US Embassy in Beijing, told media outside the court.