Kanda, a small town encircled by mountains on Japan’s southeast coast, is hundreds of miles from any major centers of business or politics. But recently, the only thing on its residents’ minds is President Trump.

In restaurants and bars and around Kanda’s small city office, people chatter nervously about the 25 percent tariffs he declared on car imports to the United States.

The reason for the anxiety is impossible to miss: The town’s lifeblood is a sprawling car factory owned by Japan’s Nissan Motor.

On a plot of land two-thirds the size of Central Park, more than 4,000 Nissan line workers produce hundreds of thousands of vehicles each year. Half of them are sold in the United States.

“We don’t really know what to make of the tariffs out here,” said Hironori Beppu, a councilor at Kanda’s chamber of commerce. “Without Nissan, Kanda’s financial situation would become really severe,” Mr. Beppu said.

Many things remain unclear about Mr. Trump’s automobile tariffs, which took effect on Thursday. Most important, how long will they stay in place? Or will the Trump administration be willing to negotiate?