New York (CNN Business) US oil prices collapsed Thursday after President Donald Trump fired another shot in the US-China trade war.

Trump's vow to impose a 10% tariff on another $300 billion of US imports from China is worrying investors that a severe economic slowdown could eat into demand for oil and other commodities. The escalation also raises the risk that China will retaliate by imposing tariffs on US oil.

Crude tumbled 8% to $53.95. That's the biggest single-day decline since February 2015. Oil was already in the red prior to Trump's tweet, which then accelerated those losses.

"This is heightening fear of a major slowdown," said Ryan Fitzmaurice, energy strategist at Rabobank.

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