Japanese stocks tumbled Thursday morning after US President Donald Trump moved forward with steeper-than-expected tariffs.

The benchmark Nikkei Stock Average opened with a sharp decline on the Tokyo stock market, at one point plunging more than 1,600 yen ($10.82), or roughly 4.55 percent, from the previous day, slipping below the critical 35,000 mark.

Investor sentiment worsened after Trump announced that the United States would implement "reciprocal tariffs" on imports from multiple countries, sparking concerns over a potential downturn in corporate earnings.

On Wednesday, Trump revealed that the US would impose a baseline 10 percent tariff on all imports, with additional levies varying by country and region. The European Union, China, the Republic of Korea and Vietnam will face tariffs of 20 percent, 34 percent, 25 percent and 46 percent, respectively. Japan will be subject to a total additional tariff of 24 percent.

The additional tariff rates will apply to approximately 60 countries and regions.

During trading hours, the Nikkei briefly dropped to the 34,100-yen range, marking its lowest level since early August. Nearly all stocks in the index declined amid a broad-based sell-off.

Hitachi Ltd fell as much as 7 percent at one point compared to the previous day, reaching its lowest price since mid-September. Major stocks, including Mitsubishi UFJ Financial Group and Toyota Motor Corporation, also saw significant losses.

Bank stocks were among the hardest hit. Resona Holdings plunged as much as 10 percent at one point, while Concordia Financial Group and Chiba Bank fell more than 6 percent.

The Nikkei Stock Average Volatility Index, or Nikkei 225 VI, which indicates the expected degree of fluctuation of the Nikkei Stock Average, surged in the morning and remained above 30. Typically, when the index surpasses 20, it signals heightened market anxiety over a potential sharp downturn.

In the Republic of Korea, the benchmark Korea Composite Stock Price Index was down around 2.7 percent at one point.

ROK's acting President Han Duck-soo has ordered emergency support measures for businesses that will be affected by the imposition of US tariffs, the Ministry of Trade, Industry and Energy said on Thursday.

Han urged the ministry to closely analyze the details and impact of the US reciprocal tariffs, while also engaging in active negotiations with Washington to minimize the effects.