Major democracies rallied together this week to issue extraordinary back-to-back rebukes of Beijing, marking a shift toward collective action and pushing back against President Xi Jinping’s strategies to position China as a global leader.

Over two consecutive days, Group of Seven leaders and North Atlantic Treaty Organization nations jointly criticized core Chinese policy under Mr. Xi as damaging to military stability, human rights, international trade and global health. NATO members vowed Monday to counter “systemic challenges to the rules-based international order” posed by China.

The one-two punch of public criticism smacks directly into Mr. Xi’s assertion that China won’t stand for lecturing by other nations, suggesting anxiety in key capitals is prompting governments to seek alignment with the U.S. over attempting to manage the relationship with Beijing on their own.

“China’s behavior changed the risk calculus,” said Evan Medeiros, a Georgetown University professor. "A very significant geopolitical threshold has been crossed.”

The international backlash comes as the Chinese Communist Party is preparing to put Mr. Xi at the center of its 100th anniversary celebration in two weeks, the successful emergence from a century of struggles and humiliation by foreign powers to become the world’s top trading nation and second biggest economy.

The broadsides from the G-7 and NATO aren’t likely by themselves to undermine Mr. Xi’s powerful standing in China, said Ryan Hass, a senior fellow at the Brookings Institution in Washington. As criticism builds against Mr. Xi in major nations, the question for China’s leadership is how much it values its international standing. In Beijing, Mr. Hass added, “It could open the aperture on the question of, are we on the right track?”

China frames criticism of its policies as U.S.-led Cold War thinking, with its diplomats confidently asserting that the East is rising and the West is in decline. Hours after the G-7 event concluded, China’s embassy in the U.K., where the summit was held, issued a point-by-point denunciation of the communiqué as distorted and slanderous.

Discontent about China has built for some time among democratic nations that are concerned about its detention of Muslim Uyghurs, undoing of freedoms in Hong Kong, coercive trade practices and military provocations against the democratic island Taiwan, and all were highlighted in the G-7’s statement. The grouping of the U.S., U.K., Germany, France, Italy, Canada and Japan also expressed concern that Beijing has lacked transparency on Covid-19, while touching generally on treatment of prisoners, internet censorship and other features of Mr. Xi’s strongman rule.

China considers each issue its own business and in its embassy retort said the G-7 “arbitrarily interfered in China’s internal affairs."

Yet, central government authorities in Beijing have so far remained largely silent.

Mr. Xi hardly needs problems with the international community, which supplies investment and creates jobs, as well as buys its exports. A resurgence of Covid-19 in China’s south is dinging confidence in the nation’s pandemic response, including China-made vaccines. China wants multinational corporations to resist calls by human-rights groups to boycott next February’s Winter Olympic Games in Beijing.

And the party’s 100th anniversary celebration is a prelude to Mr. Xi’s expected bid for a third term late next year.

President Biden vowed his China policy would feature alliance building to hold China accountable and the G-7 and NATO events marked his first opportunity to promote the vision on an international stage.

The communiqué language required buy-in from participants, including European nations that enjoy massive trade with China. European governments have usually refrained from pointed complaints about China, but in recent months bristled when Beijing imposed sanctions on European politicians, companies and think tanks.

Mr. Hass said Beijing can be expected to argue the G-7 “represents a small number of countries that do not speak on behalf of the international community.”

Chinese President Xi Jinping is seen on a screen at an event marking the 100th founding anniversary of the Communist Party of China in Shanghai on June 4.

Chinese President Xi Jinping is seen on a screen at an event marking the 100th founding anniversary of the Communist Party of China in Shanghai on June 4.

Photo: aly song/Reuters

The G-7 language was tougher on China than the document produced by the larger, 30-member NATO grouping. For instance, Taiwan went unnamed by the security alliance while the G-7 statement devoted a paragraph to calls for stability in the Taiwan Strait and neighboring seas, which China claims as its sovereign domain. It was the first-ever mention of that hot-button issue in such a communiqué, according to the University of Toronto’s G-7 Research Group.

Indeed, government-run media outlets in China mocked the G-7 by showing a rendering of Leonardo da Vinci’s painting “The Last Supper” that was widely circulated online. Titled “The Last G-7,” it showed the familiar New Testament scene but with a red cake in the shape of China in front of the Jesus character—Mr. Biden as a bald eagle in this case—directing the others, also depicted as animals.

China’s state-controlled news agency, meanwhile, described the G-7 leaders’ gathering as an “anxious show of unity” and denounced the in-person event amid a pandemic.

Before the pandemic shut down his travel, Mr. Xi relied heavily on personal appearances, and the loans of government-run banks, to expand Beijing’s influence. He used the vacuum created by former President Donald Trump’s downgrade of international groupings to emphasize China’s commitment to multilateral diplomacy in global organizations like the United Nations and World Trade Organization. But he hasn’t met another head of state in person since early 2020, according to research firm China Vitae.

China is also part of the Group of 20, where the Biden administration says it wants Beijing’s support for climate initiatives and an agreement to set a minimum international tax rate for big companies. Like other members, China enjoys an effective veto in such groups.

The G-7 and NATO positions underscore deepening divisions of their members with China that risk a new type of Cold War, says Larry Diamond, a senior fellow at Stanford University’s Hoover Institution. But he said Mr. Xi will be missing the point if he feels isolated by the statements. “The message of the G-7 is the democracies of the world are taking note of what China is doing,” he said.

But if current trends continue and the split gets bigger, it could hurt China’s leadership at home. Mr. Diamond said. “People in China may be asking who lost the United States.”

To blunt foreign criticism of its policies in the past, China has effectively relied on the lure of its massive market. Increasingly, however, Chinese leaders’ message is failing to resonate, in part because of how quickly Beijing has acted to make its market inaccessible, most recently in a dispute with Australia. “Economic success is not going to get them the plaudits that they crave,” said Scott Kennedy, a senior adviser in Washington at the Center for Strategic and International Studies.

Mr. Xi himself has added a tone of pique, saying China won’t be pushed around. He has also telegraphed the message through deputies whose new more strident tones are sometimes called “Wolf Warrior” diplomacy—to plaudits at home and chagrin internationally.

When Mr. Biden dispatched his secretary of state, Antony Blinken, to meet Chinese diplomats in Alaska in March, he was lectured in front of cameras for 16 minutes about racial problems and democratic failings in the U.S. by Beijing’s top envoy, Yang Jiechi.

Days before Mr. Biden flew to Europe, Mr. Xi appeared to soften the line, telling party cadres China the world needs to recognize a "credible, lovable, and respectable China.”

In terms of policy, however, China has shown no signs of bowing to foreign pressure, with its legislature last week approving a law that would allow Beijing to strike back at governments, companies and individuals seen as contributing to efforts by foreign governments to penalize China.

Write to James T. Areddy at james.areddy@wsj.com