In a flurry of diplomacy, Chinese President Xi Jinping has agreed environmental targets with the US, held a first formal summit with Japan and pledged friendship with Vladimir Putin, even as the Russian leader is ostracised by Western countries.

Two years since becoming head of the ruling Communist Party, Xi, an establishment scion of the country's post-1949 elite, has moved from offering his own country a "Chinese dream" to an "Asia-Pacific dream" for the region, with China at its centre.

The expansion symbolises the way the world's second-largest economy is seeking a greater global diplomatic role fitting to its commercial heft -- as other rising powers, such as the United States, have before it.

But as it further engages with the world, analysts say China will have to perform ever more complicated balancing acts to meet its international responsibilities and domestic goals.

Jia Qingguo, professor of international relations at Peking University, said Beijing is still trying to establish what its interests are and strike the right balance between them, given that they vary depending on its own complex and competing identities.

"As a developing country we want to have the right to development on the climate change issue," he said. "But at the same time, as a developed country we want to cut emissions to reduce the problem of PM 2.5," he added, referring to tiny particulates which have become an emblem of the country's pollution crisis.

"China has to take up certain responsibilities," he said. "It increasingly finds it difficult to take a free ride," stressing that if the US ignored its global responsibilities, the international system would "collapse".

- Successive summits -

Chinese state media have lauded Xi, but the Communist leader's interactions with other heads of state, at a series of summits in recent weeks, tell a more nuanced story of the challenges China faces.

Under Xi, Beijing has been increasingly assertive in pursuing territorial claims against Tokyo in the East China Sea and other neighbours in the South China Sea.

Xi's awkward meeting with Japanese Prime Minister Shinzo Abe at the Asia-Pacific Economic Cooperation (APEC) summit last week followed a narrowly-crafted agreement which both sides could spin as a victory on their own terms, and was marked by barely concealed mutual distaste, evident from images of the two leaders shaking hands.

Despite the dramatic emissions targets announced with US President Barack Obama in Beijing, the two sides made clear they hold fundamentally opposite positions on multiple issues including human rights and regional security.

Both Abe and Obama were in Beijing this month to participate in the APEC forum leaders' meeting, the first of three successive regional and global summits that culminated with the G20 summit in Brisbane, Australia -- which China will host in 2016.

China's role at the centre of proceedings contrasted noticeably with that of fellow UN Security Council permanent member Russia, whose president left the G20 early as Western countries criticised him over Ukraine and other issues.

- Compete and cooperate -

But China's potential as a diplomatic middleman is constrained by history and its domestic priorities.

Kim Han-Kwon, an expert at the Asan Institute for Policy Studies in Seoul, said that China's Communist leaders have embraced "patriotic nationalism" since the end of the Cold War to replace socialist ideology as a unifying internal glue.

As a result they are pushed "to show a more strong and stern image of China to protect China's own national interest", he said.

Before Xi and Australian Prime Minister Tony Abbott announced a deal to slash trade barriers, Obama warned of the dangers of outright conflict in Asia as China contests disputed territory.

The US, Japanese and Australian leaders committed their countries to deepening existing strong security cooperation in the Asia-Pacific -- with China the obvious object of their attentions.

Kerry Brown, professor of Chinese politics at the University of Sydney, said that Xi does not want "challenges from the external world" to distract China from internal changes such as transforming the economy towards more stable and sustainable growth.

"The question now is will the rest of the world let it do this without making more demands on it," he said.

That may be unavoidable. At the global level the US and China both compete and cooperate on issues such as climate change and the denuclearisation of North Korea, said Kim of the Asan Institute.

But he added that in the realm of "regional international politics in Northeast Asia, strategic competition between the US and China has increased".