Shares of Europe's top carmakers jumped on Wednesday after the U.S. and Japan's blockbuster trade agreement raised hopes of a tariff breakthrough for other major exporters.

In a post on social media platform Truth Social, Trump described the "massive" trade agreement as "perhaps the largest Deal ever made."

The deal is expected to mean U.S. tariffs on imported Japanese vehicles and parts will fall to 15%, a significant drop from the existing 25% rate that is levied across countries.

Japanese Prime Minister Shigeru Ishiba welcomed the trade agreement, saying it marks "the lowest figure among countries that have a trade surplus with the U.S.," according to Reuters.

The Stoxx Europe autos index rose 4.2% on Wednesday morning, putting it on track for its biggest daily gain since mid-February, according to LSEG data.

Germany's Volkswagen, BMW and Mercedes-Benz Group were all up more than 5% on the news at 9:51 am London time (4:51 am ET), while luxury automaker Porsche soared 7.5%.

Milan-listed shares of Jeep maker Stellantis was also up around 7.1%.

The gains followed a sharp upswing for Japanese autos stocks. Toyota surged over 14%, with domestic peers Honda and Nissan up 11% and 8%, respectively.

In a speech that followed his Truth Social post, Trump said the U.S. and Japan were concluding an additional deal involving liquified natural gas, adding that "we have Europe coming in tomorrow," without specifying details.

The automotive sector is widely regarded as acutely vulnerable to tariffs, particularly given the high globalization of supply chains and the heavy reliance on manufacturing operations across North America.

In Japan, auto exports to the U.S. are pivotal to the health of the world's fourth-largest economy, accounting for 28.3% of all shipments in 2024, according to customs data.

HSBC economists described the reduced U.S. auto tariff as a "massive boon" for Japan, noting that the country appears to have secured advantageous terms compared to the rest of Asia.

Citi economist Katsuhiko Aiba said Washington and Tokyo's deal to lower reciprocal and auto tariffs to 15% could influence the course of talks with other major auto exporters.

"It is notable that auto tariffs were reduced without any cap on auto exports for a major auto exporting country, which may have implications for negotiations with the EU and South Korea," Aiba said in a research note.

The European Union has long been scrambling to reach a deal with the U.S. to lower auto tariffs.

Trump, however, recently sought to ramp up pressure on the 27-naiton bloc by threatening to raise levies on EU imports to the U.S. to 30% from Aug. 1, if no agreement is reached before that time.

Rella Suskin, equity analyst at Morningstar, said it remains "impossible to predict" whether a European auto deal could follow Japan's new trade terms with the U.S., "however that is certainly what the markets are reflecting."

One critical point, Suskin said, was Japan's commitment to invest more than half a trillion dollars into the U.S.

"Will Europe do the same? While the European automakers have significant investment plans in the US in their pipeline, the figures do not come close to Japan's commitment," Suskin told CNBC by email.

"EU negotiators have also proposed removing their 10% duties on US car exports if the US reduces its duties on the sector to below 20%. The 15% duty agreed with Japan implies that a duty below 20% is viable," she added.

The U.S. accounted for 22% of the EU's export market in 2024, according to data from the European Automobile Manufacturers' Association (ACEA), an industry lobby group.

— CNBC's Lim Hui Jie contributed to this report.