Europe and China warned President Donald Trump yesterday they would respond in the event of a trade war with the US, with one Brussels official saying retaliation could also target goods from areas governed by his Republican Party.

Trump was expected later in the day to sign a proclamation imposing 25 per cent tariffs on steel imports and 10 per cent on aluminium, though a White House official said this could slide into as documents had to be cleared through a legal process.

Both Brussels and Beijing voiced hope that a trade war could be averted, and the European Commission raised the prospect that Trump could consider exempting the EU’s 28 member states from the measures along with US neighbours Canada and Mexico. Some countries advised against any overhasty reaction to Trump’s plan, which has drawn fire at home as well as rattling global financial markets, particularly Canada which as a close trading partner of the US has perhaps most to lose.

But the EU talked tough.

“If Donald Trump puts in place the measures this evening, we have a whole arsenal at our disposal with which to respond,” European Financial Affairs Commissioner Pierre Moscovici said.

Counter-measures would include European tariffs on US oranges, tobacco and bourbon, he said, adding that some products under consideration for an EU riposte were largely produced in constituencies controlled by Trump’s Republicans.

“We want Congress to understand that this would be a lose-lose situation,” Moscovici told BFM TV.

The EU is by far the biggest trading partner of the US by value and, after China, member states have together the biggest trade surplus with the country.