Some diplomats in China have voiced concerns over President Xi Jinping's possible indefinite rule, warning that Beijing is set to adopt a tougher approach toward smaller Asian countries to expand its clout in the region.

Most members of the Association of Southeast Asian Nations have maintained amicable ties with Japan, Asia's second-biggest economy after China, but they may start to keep their distance from Tokyo to protect their national interests over the next two decades, the diplomats said.

On Tuesday, the annual session of China's parliament closed, after laying the groundwork for achieving Xi's goal of turning China into a "great modern socialist country" by the middle of the 21st century.

On March 11, the National People's Congress approved the first amendment of China's Constitution in more than a decade to scrap the two-term limit for the president and vice president, paving the way for Xi to stay in office for life.

The term limits were instituted in 1982 by former leader Deng Xiaoping, as he wanted to prevent a return to the 10-year chaos of the Cultural Revolution, initiated in 1966 by Mao Zedong who remained in power until his death in 1976.

Xi's political thought was also enshrined in the nation's Constitution, sparking fears that the latest constitutional amendment heralds a return to a personal, rather than party, authoritarianism in China.

In a Cabinet reshuffle, Xi tapped his confidant Wang Qishan, who has held several key posts in the ruling Communist Party of China, as vice president, which could turn the country's long-established collective leadership system into a mere formality.

Xi was unanimously re-elected as China's president to a second five-year term by the National People's Congress on Saturday.

Western media note that Xi's ultimate goal is believed to be disseminating his political thought around the world.

"What's not in question is that Xi wants to increase his country's clout, to show the world that his model of government is a worthy alternative to those of the West," Newsweek said last week.

"Xi believes that the world should accommodate China, not the other way around," the U.S. magazine said.

Indeed, Xi said in a speech at the closure of the annual parliamentary session that Beijing "will continue to actively participate in the reform and construction of the global governance system," indicating he is keen to build a Chinese-led international order.

The Global Times, an influential tabloid affiliated with the Communist Party, suggested Beijing wants Xi's thought to spread across the globe, criticizing Western values based on democracy and capitalism.

"In these years we have seen the rise and decline of countries and particularly the harsh reality that the Western political system doesn't apply to developing countries and produces dreadful results," the newspaper said in an editorial earlier this month.

"Luckily China has maintained its steady rise for a long period. We are increasingly confident that the key to China's path lies in upholding strong Party leadership and firmly following the leadership of the Party Central Committee with Comrade Xi Jinping at the core," it added.

China's apparent readiness to expand its influence in the region has its smaller neighbors concerned.

"Given that Xi is expected to remain president for the next 20 years, how can small states like us work against China?" a diplomat in Beijing from one of the 10 ASEAN countries said on condition of anonymity. "We should not offend China to safeguard our national interests."

Amid worries over China's increasing assertiveness in nearby waters, Foreign Minister Wang Yi has been sticking to a hard-line stance, repeatedly stating China's determination "to maintain peace and stability in the South China Sea."

On the economic front, Beijing has sought to expand infrastructure networks in Asia, the Middle East, Europe and Africa to attain its goal of connecting countries along the ancient Silk Road more closely, under the "One Belt, One Road" initiative.

In an apparent move to counter the project, which some Western nations argue would only help China boost its dominance and influence worldwide, Japan has been making efforts to promote its "free and open Indo-Pacific strategy."

Japanese Prime Minister Shinzo Abe has said the concept is aimed at ensuring stability from East Asia to Africa through cooperation with countries that share values such as freedom of navigation and the rule of law.

(Abe and Xi meet for talks in Vietnam in November 2017)

Many ASEAN member states have expressed support for Abe's plan, but they have begun to reconsider whether they should uphold China's "One Belt, One Road" project or Japan's "Indo-Pacific strategy," another diplomat from an Asian nation said.

"We will not fully cooperate in the belt and road initiative, but it is difficult to say we are supporting the Indo-Pacific strategy in consideration of China," the diplomat said. "I think many small countries in the region are sharing the same view."

Malcolm Cook, a senior fellow at the ISEAS-Yusof Ishak Institute in Singapore, said, "Some Southeast Asian states have already bent to Chinese pressure."

Some foreign affairs experts have called on Abe to start mapping out a strategic policy to engage with ASEAN as soon as possible to curb Beijing's rising influence and protect Japan's interests in the region.