BEIJING: As Chinese leader Xi Jinping prepares to embark on a second five-year term this week, the impulsive leaders of North Korea and the United States could spoil his party, reports AFP.

The stability-obsessed Chinese Communist Party has left nothing to chance, ramping up security in Beijing ahead of Wednesday's opening of a congress to re-anoint Xi as general secretary.

Beyond China's borders, Xi has less control.

There, he is at the mercy of two unpredictable men, US President Donald Trump and North Korean strongman Kim Jong-Un -- a predicament that points to the limits of China's bid to project soft power. Some analysts say Kim could try to cause a stir by testing another missile or nuclear bomb in the middle of China's most important political event, which is held every five years.

A new test could trigger another 140-character salvo by Trump, who has alternated between prodding and praising Xi's response to North Korea.

Trump's mercurial Twitter diplomacy has contrasted with Xi's unemotional style. The US leader has also pointedly left Xi hanging over whether he will hit China with tariffs over trade grievances.

Despite the mixed messages, Xi has professed his friendship with Trump, confirming an invitation for the US president to come to Beijing next month, when they will discuss trade and North Korea face-to-face.

His relationship with Kim is also complicated.

The North Korean leader has already interfered with two international summits that the Chinese president has hosted this year, by staging headline-grabbing provocations.

In May, as Xi prepared to address world leaders gathered in Beijing on his signature Belt and Road initiative -- a Chinese-led trade infrastructure programme -- the North successfully launched a new ballistic missile.

Then in September, it conducted its most powerful nuclear test to date, hours before Xi took the stage for a speech before leaders of the developing world at the annual BRICS summit.

The timing was seen as a slight towards Xi and an attempt by Kim to strongarm his Chinese neighbour into convincing Trump to sit down for talks.

A new nuclear test during the party congress "would be more than a loss of face. It will harm the ruling party of China," said Cheng Xiaohe, an associate professor of international relations at Renmin University in Beijing.

"It will harm Xi Jinping at this crucial moment."

While the congress will help Xi confirm his status as China's most powerful leader in decades, he has been unable to resolve the biggest international crisis.