The mildly spoken and widely respected Sydney professor Chongyi Feng is back in Australia, much to the relief of a small band of supporters and friends who gathered at Sydney airport on Sunday morning to welcome him home.

"Great, brilliant," Dr Feng told the ABC when asked how he felt after finally stepping off his China Southern flight from Guangzhou, more than a week after Chinese officials had first prevented him from leaving.

Academic colleagues believe Dr Feng, perhaps more than any other Chinese scholar, has helped Australians understand the complex political and economic relationship with the world's most populous nation and this country's largest trading partner.

Dr Chongyi Feng's published research over a long academic career has touched upon sensitive areas. ( Supplied )

It's that invaluable, fearless, and independent work, published over decades in Australia, that has undoubtedly earned him the ire of Communist party officials in the country of his birth.

"Unfortunately a signal of intimidation has been sent to Chinese Australians not to criticise Communist party interference in Australian domestic affairs," the head of the National Security College at the Australian National University (ANU), Rory Medcalf, says.

"It's great news that he has been released and we don't know what was discussed — we may never know what was discussed — but that's understandable," he adds.

Dr Feng was finally allowed to leave Guangzho on Saturday, a month after arriving in China where he had met with fellow academics, intellectuals, and human rights lawyers in several cities.

The professor, who works at Sydney's University of Technology (UTS), has previously criticised Beijing's growing influence in Australia, particularly within Australia's Chinese-language media, and its crackdown on dissenters in China.

"The message, the signal publicly is one of intimidation towards Chinese Australians who are critical of the Chinese Government's interference in Australian domestic affairs — and that's pretty worrying," warns Professor Medcalf.

"Professor Feng is an important voice here because he shows that the concern about the influence of the Chinese Communist Party in Australia is not just one held by the Australian Government and its agencies."

The treatment of Dr Feng has also highlighted his fierce academic independence and the different focus taken by his colleagues who work inside the Beijing-supported Australia-China Relationship Institute (ACRI), which is also based at UTS in Sydney.

Throughout his career Dr Feng's research has often concentrated on pro-democracy groups in China while ACRI — which was established in 2014 — focusses on the economic relationship between both countries.

By coincidence ACRI's director, former foreign minister Bob Carr, was in China attending the Boao Forum last week when Dr Feng was told he was unable to leave the country.

In a statement Mr Carr said he'd made private representations in Beijing and Canberra about Dr Feng's case, insisting that was the best way to handle the difficult consular matter.

Threat remains for Feng's family, legal team

Dr Feng arrived in Sydney on Sunday morning. ( ABC News: Lily Mayers )

After arriving in Sydney, Dr Feng said he was not told why he was permitted to leave China, but acknowledged he was concerned about what might happen to the lawyers who had helped him there.

"I did not do anything illegal, and the lawyers only performed their duty," he told the ABC.

International law expert Don Rothwell from ANU says whatever agreement Dr Feng signed as a condition of being allowed to leave China, it would not be enforceable before an Australian court, due to "principles of private international law and the doctrine of 'foreign governmental interests'."

"In the absence of an Australia-China Extradition Treaty, Professor Feng could also not be the subject of an extradition request from China if he elected to make [a] public statement about his questioning in China," Professor Rothwell says.

However he warns there remains a threat to Professor Feng's legal team, his family, friends, and associates if he speaks in detail about his recent ordeal.

On Sunday the Australian Government "welcomed" the news Dr Feng departed China on Saturday night, but made no other comment.