"We feel America is very arrogant. They have taken a wrong action. The result is that they will hurt themselves. If they release the list of $100 billion tariffs, China is prepared. And will not hesitate," he added.

"We will immediately fight back with a major response," the representative said during a Chinese-language briefing with reporters Friday in Beijing. "We have no other choice."

If the U.S. goes through with an additional $100 billion in tariffs, China will not hesitate to fight back and is already prepared to, a Ministry of Commerce representative said.

U.S. President Donald Trump said late Thursday that he instructed the United States trade representative to consider $100 billion in additional tariffs against China. Stock index futures fell sharply after the news, with Dow futures off more than 200 points, on fears of retaliation by China.

"We believe this is a battle between unilateralism and multilateralism, a fight between protectionism and free trade," the Ministry of Commerce representative said. "This is not good for China, or the world. Facing this serious problem, we must fight resolutely."

"We have prepared with a bottom-line mindset and have planned detailed action. We won't start a war, but if someone does, we will definitely fight back," the representative said.

He added there was no merit to talk the two countries were discussing trade behind the scenes.

Thursday's announcement follows the Trump administration's late Tuesday proposal for 25 percent tariffs on imports of roughly 1,300 Chinese product lines valued at $50 billion, ranging from machinery to vaccines. Less than 24 hours later, China's Ministry of Commerce revealed a list of 106 imports from the U.S. that will be subject to a 25 percent tariff, including soybeans and cars.

No effective date for China's planned tariffs was announced at the time. The Office of the U.S. Trade Representative has planned a hearing on its proposed duties for May 15.

— CNBC's Eunice Yoon contributed to this report.