Toyota, the world's largest car manufacturer, fell 4 percent at the Tokyo Stock Exchange's opening on Thursday.
Honda, which earns more than half of its revenue from North America, lost around 3 percent. Nissan simultaneously fell 3.5 percent, while Mazda plummeted more than 5 percent.
Japan is now considering "suitable measures" in response to Trump's announcement of heavy import tariffs on cars, announces Prime Minister Shigeru Ishiba.
Of course, we will consider all alternatives, he says to the country's parliament.
Cars and car parts are Japan's main export goods to the USA and the tariffs raise concerns about the effects on the broader economy.
Trump's new car tariffs are to come into force on April 2 and apply not only to fully assembled cars but also to important car parts such as engines, gearboxes, and electrical components used in vehicles, according to the White House.
