China reached out for Europe's support in its bitter trade war with the US, leaving the EU at risk of getting entangled in a conflict with repercussions around the world.

The European Union is caught in a bind as it too shares many of Washington's grievances with Beijing's trade practices, but is also under a threat of protectionist measures ordered up by US President Donald Trump.

In a rare diplomatic plea, China on Friday called on the EU to take a joint stand against US protectionism as Trump warned that he could slap another $100 billion (86 billion euros) of extra tariffs on China's imports.

"China and the EU... should take a clear stance against protectionism, jointly preserve the rules-based multilateral trade order, and keep the global economy on a sound and sustainable track," Zhang Ming, the head of the Chinese mission to the EU, said in a statement sent to AFP.

"This is a joint responsibility of China and the EU. We must act together to make that happen," Zhang said.

The EU declined to respond directly to the envoy's invitation, insisting only that trade conflicts should be resolved at the World Trade Organization, the Geneva-based body set up to resolve disputes.

The bloc is "firm in the belief that free and fair trade is one of the most powerful engines for growth, supporting millions of jobs and contributing to prosperity," European Commission spokesman Daniel Rosario said in a response to AFP.

The EU and the US themselves nearly descended into a trade war after Trump in March threatened to impose tariffs on steel and aluminium imports that would, if confirmed, punish European manufacturers.

But Trump granted Europe a last-minute exemption, giving EU negotiators until May 1 to come up with a solution to unfair trade policies alleged by the US leader.

The Europeans reject Trump's allegations, which have mostly circled on Germany's auto industry, and prepared a list of counter-measures in case the US reverses course and slaps on the tariffs.