South Korea's exports of steel products to the United States declined nearly 19 percent from a year earlier in March, data showed on Friday, a possible outcome of heavy tariffs imposed by the Donald Trump administration on all steel imports starting last month.

Outbound shipments of steel products to the U.S. came to US$340 million in March, down 18.9 percent from the same month last year, according to the data compiled by the Korea International Trade Association (KITA), reports Yonhap news agency.

The decrease came as the Trump administration began imposing 25 percent tariffs on all steel imports on March 12 (U.S. time) as part of its broader tariff scheme aimed at reducing America's trade deficits and bolstering local manufacturing.

Washington's duty-free quotas for steel imports from South Korea and other countries have also been abolished.

Industry watchers said it is difficult to assess the impact of U.S. tariffs on Seoul's steel exports as transactions are usually made months ahead, but that there may still have been some influence.

Korean steelmakers have been devising response measures to the U.S. tariffs, with some companies planning to increase their production in the U.S.

Hyundai Steel Co. plans to invest $5.8 billion to construct an electric arc furnace-based steel mill in Louisiana by 2029, its first overseas production facility.

South Korean exports will likely come under the substantive influence of U.S. tariffs starting in the second quarter, the trade minister said, pledging "swift" support measures for affected industries.

"Local industries are feeling a growing sense of unease as unprecedented uncertainties persist," Trade Minister Cheong In-kyo said in a meeting with export-related officials, noting the impact of tariffs imposed by the Donald Trump administration is anticipated to materialize in the second quarter.

Cheong said the government will work together with related authorities to closely monitor export conditions in each region and "swiftly" devise measures to ease challenges faced by local exporters.

The government has announced plans to inject trillions of won in financial support to help exporters weather the effects of Washington's hefty tariffs on key items, including steel, aluminum and automobiles.

In the first quarter, South Korea's outbound shipments decreased 2.1 percent from a year earlier to US$159.8 billion on the weak performance of the auto and machinery sectors, according to government data.