A war between the US and China would be long, destructive and could erupt if regional disputes already underway overheat, United States President Barack Obama’s former chief intelligence adviser has warned.

David Gompert sent the warning to policy makers in a Rand Corporation report commissioned by the US Army.

“War between the United States and China could be so ruinous for both countries, for East Asia, and for the world that it might seem unthinkable,” Mr Gompert wrote.

“Yet it is not: China and the United States are at loggerheads over several regional disputes that could lead to military confrontation or even violence between them.”

“If an incident occurred or a crisis overheated, both have an incentive to strike enemy forces before being struck by them.

“And if hostilities erupted, both have ample forces, technology, industrial might, and personnel to fight across vast expanses of land, sea, air, space, and cyberspace.”

He said if such a war broke out today, China’s losses would greatly exceed that of the US.

But he said it was possible by 2025 China’s economy may have overtaken the US’s, and the gap could be much smaller.

“Even then, however, China could not be confident of gaining military advantage, which suggests the possibility of a prolonged and destructive, yet inconclusive, war,” Mr Gompert said.

US ‘should prepare for long, fierce war’

Mr Gompert said the US should make sensible preparations to wage a “long and fierce” war with China but argued it must also develop plans to limit the scope, intensity and duration of such a conflict.

His report came ahead of November’s US presidential election, in which one of the candidates, Donald Trump, has refused to rule out the possibility of conflict.

Mr Gompert said the US should make sensible preparations to wage a war with China. Photo: AAP

“I would use trade to negotiate. Would I go to war? Look, let me just tell you. There’s a question I wouldn’t want to answer,” Mr Trump said in a New York Times interview in March.

“Because I don’t want to say I won’t or I will or — do you understand that.

“That’s the problem with our country.

“A politician would say: ‘Oh I would never go to war’ or they’d say: ‘Oh I would go to war.’

“I don’t want to say what I’d do because, again, we need unpredictability.”

Australian National University defence expert Paul Dibb said: “[If Mr Trump wins the election] sure as hell … we’d have the most unpredictable America the world has ever seen.”

“It is very difficult to say things that are balanced and objective about President Trump.

“It raises whole questions about the ANZUS (Australia, New Zealand and United States Security Treaty) alliance.”