The US is "opening fire" on the world with its threatened tariffs, China warned today, saying no one wants a trade war but it will respond the instant US measures go into effect. 

The Trump administration's tariffs on $34 billion of Chinese imports are due to go into effect at 5.01am (Irish time), which is just after midday in Beijing. 

US President Donald Trump has threatened to escalate the trade conflict with tariffs on as much as $450 billion worth of Chinese goods if China retaliates.

The row has hit financial markets including stocks, currencies and the global trade of commodities from soybeans to coal. 

China has said it will not "fire the first shot", but its customs agency made clear today that Chinese tariffs on US goods would take effect immediately after US duties on Chinese goods kick in. 

Speaking at a weekly news conference, Commerce Ministry spokesman Gao Feng warned the proposed US tariffs would hit international supply chains, including foreign companies in the world's second-largest economy.

"If the US implements tariffs, they will actually be adding tariffs on companies from all countries, including Chinese and US companies," Gao said. 

"US measures are essentially attacking global supply and value chains. To put it simply, the US is opening fire on the entire world, including itself," he said. 

"China will not bow down in the face of threats and blackmail and will not falter from its determination to defend free trade and the multilateral system," he added. 

Asked whether US companies would be targeted with "qualitative measures" in China in a trade war, Gao said the government would protect the legal rights of all foreign companies in the country. 

"We will continue to assess the potential impact of the U.S.-initiated trade war on companies and will help companies mitigate possible shocks," he said. 

Gao said China's foreign trade was expected to continue on a stable path in the second half of the year, though investors fear a full-blown Sino-US trade war would deal a body blow to Chinese exports and its economy. 

Foreign companies accounted for $20 billion, or 59%, of the $34 billion of exports from China that will be subject to new US tariffs, with US firms accounting for a significant part of that 59%, Gao said. 

China's plans to impose tariffs on hundreds of US goods targets some top US exports, including soybeans, sorghum and cotton, threatening USfarmers in states that backed Trump, such as Texas and Iowa. 

Chinese buying of soybeans has already ground almost to a halt ahead of the duties. 

In the latest sign that the risk of penalties is hitting trade, a vessel carrying US coal and heading for China was diverted to Singapore. 

US carmaker Ford said today it has no plans currently to hike retail prices of its imported Ford and Lincoln models in China, despite steep additional tariffs on imported US vehicles set to come into play on Friday. 

Ford said it encouraged Washington and Beijing to resolve their issues over trade and that it would "continue to monitor the situation as it evolves".

The World Trade Organisation this week warned that trade barriers being erected by major economies could jeopardise the global economic recovery, with their effects already starting to show. 

Adding to the tensions, a Chinese court this week temporarily barred Micron Technology from selling its main semiconductor products in the world's biggest memory chip market, citing violation of patents held by Taiwan's United Microelectronics. 

Beijing has made the semiconductor sector a key priority under its "Made in China 2025" strategy, which has shifted up a gear after a US ban on sales to Chinese phone maker ZTE underscored China's lack of domestic chips. 

Both Chinese and US business sources in China said there appeared to be little hope that the tariffs could be averted. 

A senior Western diplomat told Reuters that there was no sign of any talks at the moment between the two countries, even via back channels.

The industry source said China had been unable to address the Trump administration's concerns about Chinese trade policies in at least five key areas.

These included forced technology transfers, Chinese industrial overcapacity, government subsidies, SOE reform, and Beijing's restrictions in the cloud computing industry.