China's national security concerns will take precedence over more usual diplomatic manoeuvrings in the case of detained Australian Stern Hu, a former Australian defence attache says.

Mr Hu, a Rio Tinto employee, has been accused of commercial espionage in relation to iron ore agreements and has been in custody in Shanghai for a week.

Russell Smith, formerly the Australian military attache in China, is now the regional director for strategic analysis firm IHS.

He says expectations that Australian Foreign Minister Stephen Smith can simply telephone his Chinese counterpart to sort out Mr Hu's release have to be balanced by Chinese political realities.

"A better reflection of the real state of the relationship is that we will dance to China's tune," he told Radio Australia's Connect Asia program.

"You ... need to understand where the ministry of foreign affairs sits in the pecking order. The ministry of state security is certainly a senior department and they've got primacy on this particular case.

"So unfortunately the Chinese minister for foreign affairs may not necessarily be able to comment on it because it's being led by another department."

Mr Smith says in China, "diplomacy takes a back seat when you talk about national security" and "the Chinese are clearly saying this is a case of national security".

The former attache says Mr Hu's past week "has been probably the most awful experience in his life".

"[He is] being detained by the ministry of state security, where he would have been subjected to all sorts of, I guess, what people would consider to be Cold War interrogation techniques. You know, sleep deprivation and so forth," Mr Smith said.

He says Chinese authorities have made the point they have lots of evidence, "so I think he's going to have a very, very difficult time and I'd imagine he's going to spend quite some time in jail".

Mr Smith says any western view that Mr Hu had only been engaged in commercial dealings ran into China's state-owned industry realities.

"Information that that particular state-owned enterprise has is state information," in their view, he said.

"Therefore the collection of that state information is a breach of national security, so all of a sudden, very quickly, they put two and two together and we're looking at an espionage case."

Mr Smith says only time will tell what is in store for Mr Hu.

"I think it's pretty much sealed for a period of time until both sides ... may be able to negotiate his release in quieter times," he said.