BEIJING (AFP) - An Australian national who was detained in China on national security grounds is expected to be formally charged, his lawyer said on Thursday (July 18), amid tensions between Canberra and Beijing.

Chinese-Australian author and democracy advocate Yang Jun, whose pen name is Yang Hengjun, was detained in January shortly after making a rare return to China from the United States.

The Foreign Ministry in Beijing said then that he was suspected of endangering "China's national security" - which often implies espionage allegations.

Mo Shaoping, Yang's lawyer, said his client's family picked up a formal notice in Beijing on Thursday that said Yang is suspected of endangering state security.

Yang has been moved into "criminal detention", indicating that his case is heading towards prosecution - though that is still "far away", he told AFP.

Previously, the Australian writer was held under "residential surveillance at a designated location" (RSDL), a form of detention that allows the authorities to hold people for serious crimes, such as endangering national security.

"The intensity of criminal detention is greater than RSDL," Mo explained.

The Australian embassy was told by a relative of Yang that he has already been transferred to a detention centre in Beijing, but it is seeking confirmation from the Chinese authorities, an Australian foreign affairs department spokesman told AFP.

"Australia continues to have consular access and have again asked that he be granted immediate access to his lawyers," the spokesman said.

Chinese Foreign Ministry spokesman Lu Kang said the case "is still in the process of further investigation".

"What I can tell you is that the Chinese state security organs handle this case strictly according to law, and fully protect Yang Jun's legal rights," Lu said at a regular press briefing.

Yang's detention comes amid heightened tensions between Western countries and an increasingly muscular Beijing.

Australia has traditionally been keen to avoid friction with its biggest trading partner, but tensions have escalated over security concerns and Beijing's growing presence in the Pacific.

Australia banned Huawei from participating in its 5G network last August over security fears.

Canberra has demanded that Yang be treated "fairly and transparently" and had complained about being notified only four days after his initial detention, instead of three days as required.