Germany has denounced moves by President Donald Trump to impose tariffs on US metal imports.

The country said that Europe needed a united response to the threat and echoed criticism from China that it risked undermining the global trade system. 

Donald Trump last week set import tariffs of 25% on steel and 10% on aluminium, to come into force in 15 days.

However Washington opened the way to some exemptions after pressure from allies. 

"Trump's policies are putting the order of a free global economy at risk," German Economy Minister Brigitte Zypries told Reuters over the weekend. 

"He does not want to understand its architecture, which is based on a rule-based system of open markets. Anyone, who is questioning this, is jeopardising prosperity, growth and employment," the minister said.

Earlier in Beijing, Chinese Commerce Minister Zhong Shan said any trade war with the US would only bring disaster to the world economy. 

US industries processing steel and aluminium have also criticised the tariffs as landing them with higher costs. 

Europe is the biggest exporter of steel to the US, accounting for nearly 5 million tonnes of total annual imports of about 35 million, and Brussels has warned Trump it would impose countermeasures if hit. 

In the event of any EU retaliation, Trump has threatened to also hit Europe's carmakers with import tariffs. 

Such a move would be particularly harmful for Germany, Europe's largest economy and a cornerstone of its car industry, since the US is one of its carmakers' main markets, and cars and vehicle parts are Germany's biggest source of income for goods exports. 

European Competition Commissioner Margrethe Vestager said that, if talks to secure exemptions failed, Brussels would impose countermeasures. 

"We have been building a global trading system for decades. European prosperity and millions of jobs depend on it - and Europe will not to stand idly by if someone puts the order of free world trade at risk," Vestager added.

Cherry-picking

US Commerce Secretary Wilbur Ross will urge the European Union to lower its trade barriers, US President Donald Trump said.

He described them as unfair to US farmers and industry, a view the EU firmly rejects.

The European Commission accused Trump of "cherry-picking" data to distort the debate.

The EU says Washington has not made clear how the exemption process works.

Trump said in a tweet on Saturday the United States was ready to drop its tariffs if the EU lowered its "horrific" rates on US products.

Today, he tweeted that Ross would be speaking with EU representatives about eliminating "large tariffs and barriers".

"Not fair to our farmers and manufacturers," he wrote.

Earlier in Beijing, Chinese Commerce Minister Zhong Shan said any trade war with the US would only bring disaster to the world economy.