President Joe Biden told Indo-Pacific allies on Saturday that he believes China’s increasing military assertiveness is an effort to test the region at a turbulent moment for Beijing.

Biden’s comments were caught by a hot mic after he and fellow leaders of the so-called Quad delivered opening remarks before the press at a summit he’s hosting near his hometown of Wilmington, Delaware. He said his administration sees Beijing’s actions as a “change in tactic, not a change in strategy.”

China is struggling to pull up an economy pummeled by the coronavirus pandemic and has seen an extended slowdown in industrial activity and real estate prices as Beijing faces pressure to ramp up spending to stimulate demand.

“China continues to behave aggressively, testing us all across the region, and it’s true in the South China Sea, the East China Sea, South China, South Asia and the Taiwan Straits,” Biden told Australian Prime Minister Anthony Albanese, Indian Prime Minister Narendra Modi and Japanese Prime Minister Fumio Kishida.

“At least from our perspective, we believe (Chinese President) Xi Jinping is looking to focus on domestic economic challenges and minimize the turbulence in China’s diplomatic relationships, and he’s also looking to buy himself some diplomatic space, in my view, to aggressively pursue China’s interest,” Biden added.

Starting with a trade war that dates back to 2018, China and the United States have grown at odds over a range of issues, from global security, such as China’s claims over the South China Sea, to industrial policy on electric vehicle and solar panel manufacturing.

The administration has repeatedly voiced concerns about Chinese aggression toward Taiwan and more recently on the frequent clashes between Chinese and Philippine vessels in disputed areas of the South China Sea.

At the summit, the leaders agreed to expand the partnership among the coast guards of the Quad nations to improve interoperability and capabilities, with Indian, Japanese and Australian personnel sailing on U.S. ships in the region. But U.S. officials would not say if those transits would include the contested South China Sea.

China also has longtime territorial disputes involving other claimants including Vietnam, Taiwan, Malaysia and Brunei. U.S. officials worry about China’s long-stated goals of unifying Taiwan with China’s mainland and the possibility of war over Taiwan. The self-ruled island democracy is claimed by Beijing as part of its territory.

The leaders in a joint declaration issued following their talks expressed “serious concern about the militarization … and coercive and intimidating maneuvers in the South China Sea.”

Biden last month dispatched his national security adviser, Jake Sullivan, to Beijing for three days of talks with Chinese officials. Sullivan during that visit also met with Xi.

Both governments are eager to keep relations on an even keel ahead of a change in the U.S. presidency in January. And both sides have said they remain committed to managing the relationship, following up on a meeting between Xi and Biden in San Francisco last November.

The concerns about China were raised as Biden showed off a slice of his Delaware hometown to the leaders of Australia, Japan and India.

When Biden began his presidency, he looked to elevate the Quad to a leader-level partnership as he tried to pivot U.S. foreign policy away from conflicts in the Middle East and toward threats and opportunities in the Indo-Pacific. This weekend’s summit is the fourth in-person and sixth overall gathering of the leaders since 2021.

“It will survive way beyond November,” Biden told the leaders.

The president, who has admitted to an uneven track record as a scholar, also seemed tickled to get to host a gathering with three world leaders at the school he attended more than 60 years ago. He welcomed each of the leaders individually for one-on-one talks at his nearby home before they gathered at the school for talks and a formal dinner.

“I don’t think the headmaster of this school thought I’d be presiding over a meeting like this,” Biden joked to fellow leaders.

Albanese, Modi and Kishida came for the summit before their appearances at the U.N. General Assembly in New York next week.

“This place could not be better suited for my final visit as prime minister,” said Kishida, who like Biden, is set to soon leave office.

Earlier, the president warmly greeted Kishida when he arrived at the residence on Saturday morning and gave the prime minister a tour of the property before they settled into talks.

White House officials said holding the talks at the president’s house, which sits near a pond in a wooded area several miles west of downtown, was intended to give the meetings a more relaxed feel.

Sullivan described the vibe of Biden’s one-on-one meeting with Albanese, who stopped by the house on Friday, as “two guys — one at the other guy’s home — talking in broad strokes about where they see the state of the world.” He said Biden and Albanese also swapped stories about their political careers.

The Australian leader remarked that the visit had given him “insight into what in my view makes you such an extraordinary world leader.”

Modi also stopped by the house on Saturday to meet with Biden before the leaders gathered for their joint talks.

“There cannot be a better place than President Biden’s hometown of Wilmington to celebrate the 20th anniversary of the Quad,” Modi said.

Biden and Modi discussed Modi’s recent visits to Russia and Ukraine as well as economic and security concerns about China. Modi is the most prominent leader from a nation that maintains a neutral position on Russia’s invasion of Ukraine.