Japanese exports suffered their steepest drop in more than four years last month as tariffs imposed by US President Donald Trump bit, official data showed Wednesday.

The year-on-year drop of 2.6 percent in July included a 10.1-percent plunge in exports to the United States, the finance ministry data showed.

Japanese exports of motor vehicles -- cars, buses and trucks -- to the world's biggest economy plummeted by 28.4 percent, while those of auto parts fell 17.4 percent.

Trump has imposed painful import tariffs on countries around the world in an attempt to boost US manufacturing and reduce the colossal US trade deficit.

On close ally Japan, Trump initially imposed across-the-board levies of 10 percent as well as tariffs of 27.5 percent on cars.

Japan's automobile industry, which includes giants like Toyota and Honda, accounts for around eight percent of the country's jobs.

Japan last month secured a trade deal that cut a threatened 25 percent "reciprocal" tariffs to 15 percent.

The rate on Japanese cars was also cut to 15 percent, although to Tokyo's consternation, this has yet to take effect.

Data last week showed that the world's fourth-biggest economy eked out better-than-expected annualised growth of 1.0 percent in the second quarter.