Tesla’s global car sales fell sharply in the second quarter, continuing a decline that began last year, as the company puts a greater emphasis on autonomous driving instead of new models aimed at attracting car buyers.

The company said it delivered 384,000 vehicles from April through June, down from 444,000 a year earlier. Tesla’s limited and aging lineup has not been able to withstand growing competition from relatively young Chinese carmakers like BYD and established Western companies like General Motors, Volkswagen and BMW.

Elon Musk, Tesla’s chief executive, has been seemingly indifferent to slumping vehicle sales, saying the company’s future lies with technology that will allow Teslas to operate autonomously and function as driverless taxis. Significant numbers of investors have bought into that vision and pushed up Tesla’s stock market valuation to more than $940 billion.

Wall Street had expected a decline in sales, and Tesla shares rose in early trading on Wednesday.

Last month, Tesla began a closely watched test of Mr. Musk’s self-driving ambition. Specially equipped Model Y sport utility vehicles, which Tesla calls Robotaxis, began offering paid rides to handpicked guests in Austin, Texas.

The guest riders, mostly Tesla enthusiasts with many social media followers, posted almost uniformly glowing reviews online. However, videos they shot betrayed some flaws in the technology, including instances when the cars braked suddenly, dropped off passengers in the middle of intersections or required intervention from safety monitors who rode in the front passenger seats.

Last week, in another milestone, a Tesla with nobody inside drove itself from the company’s factory in Austin to a customer about half an hour away. “There were no people in the car at all and no remote operators in control at any point. FULLY autonomous!” Mr. Musk wrote on X. Critics noted that videos posted by Tesla showed the car parking at the destination along a curb painted red and marked, “No Parking Fire Lane.”

Slumping car sales are certain to weigh on Tesla’s profit. The company is already close to losing money. The company would have reported a loss in the first quarter if not for the $447 million it earned from selling clean air credits to rivals whose vehicles exceeded pollution limits. The Trump administration is trying to eliminate those credits.

The sales numbers suggest that Tesla factories are operating well below potential, a further drain on profit. Tesla factories in California, Texas, China and Germany are capable of producing 2.35 million cars a year, according to the company, or about 590,000 per quarter. During the first quarter, Tesla produced 362,615 cars, meaning the factories were operating at about 62 percent of their capacity.

Production increased in the second quarter, Tesla said Wednesday, suggesting that factories were operating at 70 percent capacity. But lines that produce the Cybertruck pickup, the Model S luxury sedan and Model X sport utility vehicles appear to be operating well below their potential.

Tesla is capable of producing 225,000 of those models a year, according to company figures, or about 56,000 per quarter. In the second quarter, Tesla produced just 13,400.

Tesla had said it would begin producing a lower-cost model by the end of June, but it has not yet displayed a prototype or said when it would go on sale.

The average capacity utilization rate in the United States for the auto industry, including suppliers, is 65 percent, according to the Federal Reserve Bank of St. Louis. That is well below levels that analysts consider healthy.

Automakers have certain fixed costs like maintenance, taxes, loan interest and energy. As a result, factories that are not churning out a lot of cars typically earn modest profits or lose money.

Unused capacity may be an especially big problem for Tesla because its production is highly automated and depends on costly machinery that requires maintenance and loses value over time, said Ferdinand Dudenhöffer, director of the Center Automotive Research in Bochum, Germany.

“You can’t lay off machines,” he said. “You have to keep paying them even when you’re not using them.”

Data available before Wednesday had already signaled trouble for Tesla, whose share price has dropped about 20 percent this year.

In Britain and continental Europe, registrations of new Tesla cars fell 28 percent in May, according to the European Automobile Manufacturers’ Association, despite the introduction of an updated version of the Model Y, the company’s most popular model.

In the United States, Tesla sales fell 21 percent in the second quarter, according to estimates by Cox Automotive, a research firm.

Mr. Musk’s involvement in right-wing politics and his support of President Trump have been a factor in Tesla’s weak sales by alienating many liberals who are more likely than conservatives to buy electric vehicles.

The two men have since fallen out in a big way because of Mr. Musk’s opposition to the president’s policy bill, which slashes federal support for products that Tesla makes including solar panels, batteries and electric vehicles.

On Tuesday their dispute accelerated, with Mr. Musk threatening to finance primary challenges to Republicans who vote for the bill and Mr. Trump threatening to cut what he said were subsidies that Mr. Musk’s companies receive.

It is unclear whether liberals’ animosity toward Mr. Musk will fade because of his feud with the president.

Melissa Eddy contributed reporting.