The court's ruling invalidated some tariffs the Trump administration had imposed on Asian export powerhouses - from China and South Korea to Japan and Taiwan, the world's largest chipmaker and a key player in tech supply chains.
Within hours, Trump said he would impose a new 10 per cent duty on US imports from all countries starting on Tuesday, which he raised to 15 per cent on Saturday.
The levies, under a different law, are set for 150 days, prompting analysts to warn more measures could follow, threatening further confusion for businesses and investors.
Before the ruling, Trump's tariff push had strained Washington's diplomatic relations across Asia, particularly for export-reliant economies integrated into US-bound supply chains.
In Japan, a government spokesman said on Saturday Tokyo "will carefully examine the content of this ruling and the Trump administration's response to it, and respond appropriately".
On Sunday, Itsunori Onodera, an executive of Prime Minister Sanae Takaichi's Liberal Democratic Party and a former defence minister, called Trump's new tariffs "outrageous".
"As an ally, I'm worried this will only accelerate countries distancing themselves from the US," Onodera, the LDP tax policy chief, who is not in government, told a talk program on Fuji Television.
China, which will host Trump in late March, has not responded to the latest tariff moves, with the country on an extended holiday.
But a senior financial official in China-ruled Hong Kong described the US situation as a "fiasco".
Christopher Hui, Hong Kong's secretary for financial services and the treasury, said Trump's new levy underscored Hong Kong's "unique trade advantages".
"This shows the stability of Hong Kong's policies and our certainty ... it shows global investors the importance of predictability," Hui told a media briefing on Saturday when asked how the new tariffs would affect the city's economy.
Hong Kong has been shielded from direct exposure to US tariffs targeting Chinese goods as it operates as a separate customs territory from mainland China.
While Washington has imposed duties on mainland exports, Hong Kong-made products have generally faced lower tariff rates, allowing the city to maintain trade flows despite Sino-US tensions.
As Trump's levies escalated through 2025 and early 2026, corporate disclosures showed firms across the Asia-Pacific region reporting financial hits, supply shifts and withdrawals.
Friday's ruling concerns only the tariffs launched by Trump based on the International Emergency Economic Powers Act, intended for national emergencies.
Trade policy monitor Global Trade Alert estimated the ruling by itself cuts the trade-weighted average US tariff almost in half, from 15.4 per cent to 8.3 per cent.
For those countries with higher US tariff levels, the change is more dramatic. For China, Brazil and India, it will mean double-digit percentage-point cuts, although to still-high levels.
The Taiwanese government said it was monitoring the situation closely, noting the US government had yet to determine how to fully implement its trade deals with many countries.
"While the initial impact on Taiwan appears limited, the government will closely monitor developments and maintain close communication with the US to understand specific implementation details and respond appropriately," a cabinet statement said.
Taiwan signed a memorandum of understanding with the US in January that committed Taiwan to invest $US250 billion ($A354 billion), and a deal in February to lower what Trump calls "reciprocal" tariffs.
Even before Trump raised his new levy to 15 per cent, analysts said the court ruling might offer little relief for the global economy.
They warned of looming confusion as trading nations braced for moves by Trump to find other means of using levies to circumvent the ruling.
Thailand's Trade Policy and Strategy Office head Nantapong Chiralerspong said the ruling could benefit the country's exports as uncertainty drove a fresh round of "front-loading", where shippers race to move goods to the US, fearing even higher tariffs.
