Canada, Mexico and China have vowed to retaliate after tariffs on goods entering the US from their countries came into effect on Tuesday.
US President Donald Trump has imposed 25% tariffs against Canada and Mexico, and 20% tariffs against China.
Stock markets in the US, UK and Asia dipped following the introduction of the taxes amid fears of trade war widening.
Analysts have warned tariffs could push up prices for US households and could also have a knock on effect on consumers across the world, including the UK.
Trump threatened to impose the tariffs, which are a tax added to a product when it enters a country – on Canada, Mexico and China in response to what claims is the unacceptable flow of illegal drugs and illegal immigrants into the US.
But Canadian Prime Minister Justin Trudeau said his country was responsible for less than 1% of fentanyl entering the US and would retaliate with 25% tariffs on $150bn worth of US goods.
China swiftly announced its own counter measures, which include 10-15% tariffs on some US agricultural goods, including wheat, corn, beef and soybeans. Mexico is expected to announce its response later.
The three major stock market indexes in the US sank following the news, while the FTSE 100 index of the UK’s biggest publicly-listed companies opened sharply lower on Tuesday and stock markets in Asia were also down.
Andrew Wilson, from the International Chamber of Commerce, said: “What we’re seeing is the biggest effective increase in US tariffs since the 1940s – with severe economic risks attached to that.”
“The initial market moves are entirely reflective that we’re now entering into a very risky scenario for global trade and for the global economy,” he told BBC Radio 4’s Today programme
He said Yale University had predicted these measures could cost US households in the region of $2,000 in this year alone.
Ella Hoxha, head of fixed income at Newton Investment Management, told the BBC: “In terms of consumers, you’re more likely looking at, certainly over the short term, increases in prices as companies pass some of those prices onto the consumer.”
Chris Torrens, vice president of the British Chamber of Commerce in China, added: “It’s a huge challenge for British business because of the historical links that the UK and the US have. [We are] Seeing what looks like the dismantling of a transatlantic alliance between the US and Europe.
“But, there is a real sense of hope for a stronger UK-China relationship.”