US President Barack Obama's campaign lashed Mitt Romney for "hypocrisy" on China Friday, claiming his tough talk was undermined by his business record of shipping US jobs to the Asian giant.

The Democratic counter-punch came a day after Romney hammered Obama's record on China, and renewed his promise to brand it a currency manipulator on his first day in office in remarks which drew a stern rebuke from Beijing.

Obama's campaign enlisted former Democratic governor Ted Strickland of vital swing state Ohio, which has seen thousands of manufacturing jobs migrate to developing economies abroad, to press the president's attack.

"Governor Romney's hypocrisy apparently knows no end. He claims that he'll crack down on China but he's never done that and I don't think he ever will," Strickland said, unloading criticism on Romney's past as a venture capitalist.

"The truth is, Mr Romney's made a fortune investing in firms that specialize in shipping jobs to China and other low wage countries.

"Romney's economic philosophy was simple, and hasn't changed: profits over people, even if that means Americans lose their jobs," Strickland said on a conference call with reporters.

The Obama campaign also debuted a new advertisement which will air in nine battleground states which plowed similar ground to Strickland and accuses Romney of investing some of his fortune in China.

Romney spokeswoman Andrea Saul however said that Obama's policies towards Beijing had deepened the misery of Americans stuck in the slow economic recovery.

"They've cost hundreds of thousands of jobs and left American manufacturing in decline. As president, Mitt Romney will take immediate action to stop China's cheating and protect American jobs here at home," she said.

Romney had launched his own attack on China on Thursday, branding Beijing a cheat because of its currency and trade policies.

"The cheating takes on a lot of different dimensions," Romney said.

"The president's had the chance year after year to label China a currency manipulator, but he hasn't done so. And I will label China the currency manipulator they are on the first day."

Romney's remarks were met with a stinging response in a commentary carried by China's official Xinhua news agency.

"It is advisable that politicians, including Romney, should abandon ... short-sighted China-bashing tricks and adopt at least a little bit of statesmanship on China-US ties," the commentary said.

The unnamed author also warned a trade war would likely break out if Romney took office and honored his threat to label China a currency manipulator, and also accused the former Massachusetts governor of hypocrisy.

"It is rather ironic that a considerable portion of this China-battering politician's wealth was actually obtained by doing business with Chinese companies before he entered politics."

Strickland seized on that comment to make a wider point about Romney's foreign policy credentials.

"If even the Chinese government is willing to publicly call out this hypocrisy, how can we expect them to take him seriously if he were president?"

China bashing is a regular feature of US election campaigns, but once in office, presidents have a habit of following decades-long US foreign policy orthodoxy of seeking cooperation with Beijing.

Top Chinese leaders have told Obama that they expect a measure of anti-Beijing rhetoric in the US election, US officials have said.

But the Xinhua commentary appeared to be a shot across Romney's bow and suggest a rocky period for Sino-US relations if he comes from behind to beat Obama in the election on November 6.