U.S. President Joe Biden opened a brief visit to Vietnam on Sunday by telling the country’s leadership that the two nations have a chance to shape the Indo-Pacific for decades to come.

Mr. Biden said he hoped progress could be made on climate, the economy and other issues during his 24-hour visit.

“Vietnam and the U.S. are critical partners at what I would argue is a very critical time,” Mr. Biden told Nguyễn Phú Trọng, general secretary of the Communist Party of Vietnam, during the public portion of their meeting at party headquarters.

Mr. Trọng agreed that their meeting presented an “excellent opportunity“ to expand bilateral ties. He thanked Mr. Biden for inviting him to visit Washington soon.

Vietnam is elevating its relationship with the U.S. to the status of being a comprehensive strategic partner, which one of Biden’s top national security advisers said represents Vietnam’s highest tier of international partnership.

Other countries that Vietnam has extended the designation to include China and Russia. Elevating the U.S. to the same status suggests that Vietnam wants to hedge its friendships as U.S. and European companies look for alternatives to Chinese factories.

Mr. Biden, who arrived in Hanoi on Sunday afternoon, said last month at a fundraiser in Salt Lake City that Vietnam doesn’t want a defense alliance with the U.S., “but they want relationships because they want China to know that they’re not alone” and can choose its own partners. The president decided to tack a visit to Vietnam on to his trip to India for the Group of 20 summit that wrapped up Sunday.

With China’s economic slowdown and President Xi Jinping’s consolidation of political power, Mr. Biden sees an opportunity to bring more nations — including Vietnam and Cambodia — into America’s orbit.

“We find ourselves in a situation where all of these changes around the world are taking place,” Mr. Biden explained last month about Vietnam. “We have an opportunity, if we’re smart, to change the dynamic.”

Mr. Biden was welcomed with a pomp-filled ceremony outside the mustard-colored Presidential Palace. Scores of schoolchildren lined the steps waving small U.S. and Vietnam flags and Mr. Biden watched from an elevated review stand as high-stepping members of the military marched past. The president waved to the children before he got into his limousine to go to Communist Party headquarters to meet with Trong.

The president and Trong expressed mutual happiness over seeing each other again after last meeting some eight years ago in Washington, said Mr. Biden, who was vice president at the time.

Trong sought to flatter Mr. Biden, who faces persistent questions at home about being 80 years old and running for reelection next year.

“You have nary aged a day, and I would say you look even better than before,” Trong said. “I would say every feature of you Mr. President is complementing your image.” Mr. Biden chuckled in response.

Earlier Sunday, Jon Finer, Mr. Biden’s chief deputy national security adviser, said the elevated status represents Vietnam’s highest tier of international partnership.

“It’s important to make clear that this is more than words,” Finer told reporters aboard Mr. Biden’s flight to Hanoi. “In a system like Vietnam, it’s a signal to their entire government, their entire bureaucracy about the depth and cooperation and alignment with another country that is possible.”

Finer noted a five-decade arc in U.S.-Vietnam relations, from conflict during the Vietnam War to normalization and Vietnam’s status as a top trading partner that also shares Washington’s concerns over security in the South China Sea.

“We will be deepening that relationship through this visit,” he added.

Finer also addressed reports that Vietnam was pursuing a deal to buy weapons from Russia, even as it sought deeper ties to the United States. Finer acknowledged Vietnam’s lengthy military relationship with Russia and said the U.S. continues to work with Vietnam and other countries with similar ties to Russia to try to limit their interactions with a nation the U.S. accuses of committing war crimes and violating international law with its aggression in Ukraine.

U.S. trade with Vietnam has already accelerated since 2019. But there are limits to how much further it can progress without improvements to the country’s infrastructure, its workers’ skills and its governance. Nor has increased trade automatically put the Vietnamese economy on an upward trajectory.

Commerce Secretary Gina Raimondo said that the CEOs she talks with rank Vietnam highly as a place to diversify supply chains that before the pandemic had been overly dependent on China. Raimondo has been trying to broaden those supply chains through the Indo-Pacific Economic Framework, an initiative Mr. Biden launched last year.

“Whether it’s Vietnam or Malaysia, Indonesia, India, companies are really taking a hard look at those countries as places to do more business,” Raimondo said. “It is also true that they need to improve their workforce, housing, infrastructure and, I’d say, transparency in government operations.”

Vietnam’s economic growth slipped during the first three months of 2023. Its exporters faced higher costs and weaker demand as high inflation worldwide has hurt the market for consumer goods.

Still, U.S. imports of Vietnamese goods have nearly doubled since 2019 to $127 billion annually, according to the Census Bureau. It is unlikely that Vietnam, with its population of 100 million, can match the scale of Chinese manufacturing. In 2022, China, with 1.4 billion people, exported four times as many goods to the U.S. as did Vietnam.

There is also evidence that China is still central to the economies of many countries in the Indo-Pacific. A new analysis from the Peterson Institute of International Economics found that countries in IPEF received on average more than 30% of their imports from China and sent nearly 20% of their exports to China. This dependence has increased sharply since 2010.

White House national security adviser Jake Sullivan saw an opening to broaden the U.S. relationship with Vietnam when one of its top officials, Lê Hoài Trung, visited Washington on June 29.

After talking with Trung, Sullivan walked back to his office and decided after consulting with his team to issue a letter to the Vietnamese government proposing that the two countries take their trade and diplomatic relations to the highest possible level, according to an administration official who insisted on anonymity to discuss the details.

Sullivan picked the issue back up on July 13 while traveling with Mr. Biden in Helsinki, speaking by phone with Trọng, the general secretary of the Communist Party of Vietnam.

At a fundraiser at a barn in Maine a few weeks later, Mr. Biden went public with the deal.

“I’ve gotten a call from the head of Vietnam, desperately wants to meet me when I go to the G-20,” Mr. Biden said. “He wants to elevate us to a major partner, along with Russia and China. What do you think that’s about?”