Copper prices surged by more than 5% in New York — leaping further above other global benchmarks — as US President Donald Trump suggested imports of the metal could be subject to a 25% tariff.

Trump’s comments — made in a speech to Congress Tuesday — sparked a frenetic rally in Comex copper prices in Asian hours, as traders reacted to the possibility that tariffs on the metal could be larger than expected, and come much sooner.

Last week, Trump announced that the Commerce Department would undertake a sweeping investigation that could lead to levies on copper on national security grounds. That triggered a sharp rally in Comex prices, opening up a widening gap with equivalent prices in London and Shanghai.

The investigation could take months and the size of the tariffs was not spelled out, but Trump on Tuesday said that he’d ordered for the metal to draw a 25% levy, alongside aluminum and steel.

“I have also imposed a 25% tariff on foreign aluminum, copper and steel,” he said in his address to Congress. “Tariffs are about making America rich again. It is happening and it will happen rather quickly.”

The US president has already signed an executive order to impose that levy on aluminum and steel from March 12.

“A 25% tariff was clearly not what the market was expecting before those comments, and now traders are scrambling to price in the correct level, whatever that might end up being,” said Ole Hansen, head of commodity strategy at Saxo Bank AS. “Whatever the final tariff is, the disruption to global trade flows is very real.”

The surge on the Comex also triggered a smaller rally on the London Metal Exchange, with three-month prices jumping as much as 2.4%. For months, New York futures have been trading at a hefty premium to the LME as investors have priced in the growing likelihood of tariffs, and the additional surge on Wednesday left Comex copper trading about 11.5% higher than the LME, nearing a peak of about 13% seen last month.

The huge differential has already triggered a worldwide hunt for copper that can be shipped to the US before any tariffs are imposed, and traders are likely to redouble those efforts following Wednesday’s fresh surge.

With LME prices hovering around $9 500 a ton and New York prices trading about $1 000 higher, the arbitrage presents a huge opportunity for a market used to operating on razor-thin margins.

Comex copper stockpiles — which surged after a similarly large price spike on the exchange last year — have been drawing down in recent days, indicating that US manufacturers may also be looking to stock up before tariffs come into effect. Meanwhile, requests to withdraw the metal from the LME have surged.

Other metals were also higher on the LME, with zinc adding 2% and aluminum gaining 1.2%.