In an interview with the Wall Street Journal published on Sunday, Lou said, "Trump is an irrational type. If he were to do this, that would be in violation of the rules set by the World Trade Organisation."
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Lou said that if the United States put Trump's proposal into effect, it "would not be entitled to its position as the world’s major power. The US needs to recognise that the US and China are mutually dependent on each other. Our economic cycles are intertwined."
He acknowledged that rhetoric in a US presidential campaign can become heated.
China is the United States' largest trading partner.
Chinese officials have generally avoided criticising Trump directly, though they have made indirect criticism of his proposal to ban Muslims from entering the United States and indirectly rebuffed Trump's claims that China is stealing US jobs.
China's tightly-controlled state media has largely stuck to reporting the facts about Trump, with some notable exceptions.
Last month, influential tabloid the Global Times accused Trump of being a racist, warning that other extremists, such as Benito Mussolini and Adolf Hitler, had both been voted into power.
Trump on Sunday again asserted that China had waged "economic war" against the United States.
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"They've taken our jobs, they've taken our money," the billionaire businessman said at a campaign rally in New York. "We can't continue to be ripped off like we're being ripped off."
At a Republican presidential debate last month, Trump said China will not allow free trade or US manufacturers to compete freely.
"The 45 percent (tariff) is a threat that if they don't behave, if they don't follow the rules and regulations so that we can have it equal on both sides, we will tax you," he said.
Republican rival Ted Cruz criticized the 45 percent tariff proposal, saying during the same debate that it would be passed on to US consumers.
"How does it help you to have a president come and say ... I'm going to put a 45 percent tax on diapers when you buy diapers, on automobiles when you buy automobiles, on clothing when you buy clothing. That hurts you," the US senator from Texas said.
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The United States reported a $366-billion trade deficit with China in 2015, up from $343 billion in 2014 - the largest US trade imbalance with any nation. The deficit is up nearly 12 percent in the first two months of 2016 to $57 billion.
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