Prime Minister Scott Morrison has rubbished suggestions an Australian citizen detained in China has been working as a spy.

Key points: Yang Hengjun has pleaded with the Prime Minister to help him get home "as soon as possible"

Yang Hengjun has pleaded with the Prime Minister to help him get home "as soon as possible" He has been in detention in China on suspicion of espionage for seven months

He has been in detention in China on suspicion of espionage for seven months Scott Morrison said suggestions Dr Yang had acted as a spy were "absolutely untrue"

Sydney academic Yang Hengjun was formally arrested earlier this week on suspicion of espionage more than seven months after Chinese authorities detained him.

Mr Morrison's comments come as Dr Yang made an appeal to the Prime Minister to "help me go home as soon as possible".

China has issued repeated stern warnings to Australia to respect its legal processes, which Mr Morrison insisted his Government was doing.

"But these suggestions that he's acted as a spy for Australia are absolutely untrue," the Prime Minister told Channel Nine.

"And we'll be protecting and seeking to support our citizen, as we've been doing now for some period of time. We make no apologies for standing up for one of our citizens."

Dr Yang, 54, had been under investigation for harming China's national security, but Australian diplomats were notified he was under suspicion of committing crimes of espionage.

Australian consular staff met with Dr Yang after Chinese officials officially arrested him earlier this week.

"I am deeply indebted to the Australian embassy for coming to see me," Dr Yang said in a statement released via an Australian consular official.

"An [Ministry of State Security] investigation officer told me that Australia was small and wouldn't care about me.

"He said Australia was dependent on China for its trade and economy, and Canberra wouldn't help me, let alone rescue me. He said Australia wouldn't help because I am not white.

"This is nonsense. He was wrong. I am extremely grateful to the Australian Prime Minister, Foreign Minister and members of Parliament, the embassy team, and the ambassador for their help."

Writer Yang Hengjun has been in detention in China for more than seven months. ( Supplied: Twitter )

Under Chinese law, the penalties for espionage range from three years in jail to the death penalty.

Dr Yang had been living with his family in New York, where he was a visiting scholar at Columbia University.

He flew to the Chinese city of Guangzhou with his wife, Yuan Ruijuan, and child in January this year.

Dr Yang's family were allowed to board their connecting flight to Shanghai, but authorities escorted him from the airport.

The Prime Minister dismissed suggestions from Beijing that Australia was not respecting its legal processes, by questioning Dr Yang's detention.

"I am concerned [about his treatment], and those concerns have been raised directly by the Foreign Minister on several occasions now, and we'll continue to raise those concerns as is appropriate," Mr Morrison said.

"That's not interfering in a system, we would expect the same to occur if other countries had concerns about anyone's treatment in Australia to raise issues, and that's the way these issues should be handled.

"They have their system of justice in China, it may be different to ours, but they're a sovereign nation, and we respect that, but we do expect Australia, and indeed all citizens, to have their human rights appropriately looked after."

Chinese Foreign Ministry spokesman Geng Shuang said Dr Yang's case was being progressed but urged Australian politicians against intervening.

"The Chinese state security [agency] handle the case in accordance with the law and fully guarantee the various rights of Yang Hengjun," he said.

"The remarks made by some people in Australia are unfounded and extremely irresponsible.

"I want to reiterate that China is a country ruled by law. We urge the Australian side to earnestly respect China's judicial sovereignty, stop hyping and [adding] pressure, and to not intervene in China's law-based handling of the case in any way."

ABC/AP