Harley-Davidson has announced plans to shift some manufacturing of its iconic motorcycles overseas to avoid retaliatory European tariffs imposed last week.

The firm suggested it had no choice after the European Union hit American motorcycles with duties of 31% on Friday, up from 6%, boosting the cost to EU consumers by about $2,200.

The EU targeted the US vehicles as part of its rebuttal to President Donald Trump's tariffs on imported aluminum and steel, one aspect of his multi-front trade war.

Moving production overseas is expected to require nine to 18 months, so in the near term, Harley-Davidson will absorb the costs of EU tariffs, the company said in a regulatory notice.

That will add an estimated $90m to $100m annually.

President Trump expressed his disappointment in a tweet saying: "Surprised that Harley-Davidson, of all companies, would be the first to wave the White Flag."

The company said; "Increasing international production to alleviate the EU tariff burden is not the company's preference but represents the only sustainable option to make its motorcycles accessible to customers in the EU and maintain a viable business in Europe." 

Some analysts expect to see more instances of company shifts in supply chain or manufacturing venues due to trade tariffs when the second-quarter earnings season kicks off in early next month.

Republican Senator Ben Sasse placed the blame squarely on Mr Trump's shoulders.

"The problem isn't that Harley is unpatriotic - it's that tariffs are stupid. They're tax increases on Americans, they don't work and apparently we're going to see more of this," he said.

Harley-Davidson currently has overseas manufacturing plants in Australia, Brazil and India. It is building a plant in Thailand.

The company did not specify where the additional manufacturing would go.

"We are currently assessing the potential impact on our US facilities," said Harley-Davidson spokesman Michael Pflughoeft.

"We are hopeful the US and EU governments will continue to work together to reach an agreement on trade issues and rescind these tariffs."

On Wall Street, Harley-Davidson shares dropped sharply 5.97%.

Harley-Davidson has been relying on Europe and other international markets to help offset declining sales in the US, where the baby boomers who have long bought the vehicles are getting older and younger consumers are not taking to the motorcycles in a big way.

In the first quarter, retail sales of motorcycles fell 12% in the United States but rose nearly 7% in the European/Middle East/Africa region.

In the wake of the sluggish US sales, Harley-Davidson announced in January it would close its Kansas City, Missouri assembly plant and consolidate jobs in York, Pennsylvania.

Adding to the difficulty facing the company were steel and aluminium tariffs on the EU, Canada and Mexico finalised by the Trump administration in early June.

Chief financial officer John Olin told analysts in April he expected the tariffs to add $15m to $20m "on top of already rising raw materials", representing "quite a headwind for the company over the next several quarters".