Republican presidential hopeful Mitt Romney on Saturday turned rival Jon Huntsman's service as US ambassador to China against him Saturday -- and drew a rare rebuke in Mandarin in response.

The unusual -- and unusually sharp -- clash came during a prime-time debate among the candidates to be the party's standard-bearer to take on President Barack Obama in the November 6 elections.

After Huntsman warned against slapping retaliatory tariffs on Chinese goods in response to allegedly unfair trade practices, Romney pounced: "You were, the last two years, implementing the policies of this administration in China."

"The rest of us on this stage were doing our best to get Republicans elected across the country and stop the policies of this president from being put forward," the former Massachusetts governor added.

"And if I'm president of the United States, I'm not going to continue to talk about how important China is and how we have to get along. And I believe those things. They're very important. And we do have to get along," said Romney.

"But I'm also going to tell the Chinese it's time to stop. You have to play by the rules. I will not let you kill American jobs any longer," he added, to applause from the crowd.

"I think it's important to note, as they would say in China that," Huntsman began, before shifting briefly to Mandarin Chinese, then translating himself "he doesn't quite understand this situation."

"What he is calling for would lead to a trade war. It makes for easy talk and a nice applause line but it's far different from the reality in the US-China relationship," said the former ambassador.

Huntsman called for "a logical, sensible conversation" with Chinese leaders to avert a trade war that would hurt US exporters "in a time when this nation can least afford a trade war."

Romney cast doubt on whether Beijing would actually retaliate, saying "the last thing China wants is a trade war" and adding "they don't want it real bad" because they sell more in US markets than US exporters sell there.

"We've been listening for 10 years from people talking about how we can't hold China to the rules of free and fair trade and if I'm president I will hold them to those rules," he said.

"And we'll respect each other -- but we are not going to let them just run all over us and steal our jobs," he said.

Criticisms of China are staples of US presidential election campaigns, but tough rhetoric before an electoin often melts away when the candidate becomes president.