The two nations are historical allies, with Mao Zedong famously likening their brotherly ties to being “as close as lips and teeth”. But the ratcheting up of North Korean aggression – including its two recent tests of intercontinental ballistic missiles (ICBMs) and Saturday’s launch of short-range missiles – poses a serious dilemma for China.

What is the relationship between China and North Korea?

The two nations are long-standing allies, sharing not only a border more than 1,400km long, but significant economic and diplomatic ties.

China and North Korea are still bound by a 1961 defence treaty for “mutual aid and cooperation” that is up for renewal in 2021. Additionally, China remains North Korea’s largest trading partner – accounting for around 90 per cent of its foreign trade – and provides an essential economic lifeline for the hermit kingdom.

Beijing has been criticised for its reluctance to put economic pressure on Pyongyang, but has agreed to various United Nations resolutions to enact sanctions on the regime, including suspending trade in coal. Most recently, China voted with the UN Security Council to tighten pressure on North Korea by cutting off iron ore, iron, lead and coal.

How has China’s relationship with North Korea changed over the past few decades?

Despite their shared communist roots and brothers-in-arms fighting during the Korean war, Sino-North Korean relations have fluctuated over the last few decades. For example, during the Cultural Revolution, the Chinese Red Guards would mockingly call Kim Il-sung a “fat revisionist”.

But the relationship has been in a downswing in recent years. North Korea’s leader today, Kim Jong-un, is the only head of the country who has not travelled abroad or met his Chinese counterpart since assuming power, in contrast to his father Kim Jong-il, who travelled to China multiple times during his rule.

Observers say their relationship has been further strained by Kim Jong-un’s unpredictable and bellicose behaviour, highlighted by the 2013 execution of his uncle, followed by the apparent assassination of his half-brother Kim Jong-nam, who had been living in exile in Macau, an autonomous region in China.

What are the fears and worries of China regarding North Korea now?

China has many concerns about the situation on the Korean peninsula, and chief among them is the destabilisation of the North Korean regime. If Kim’s regime collapses, Beijing would have to cope with the ensuing chaos from an influx of millions of North Korean refugees across its northern border, as well as the possibility of a reunified Korea friendly to the US, with an American military presence.

As a result, China has been cautious about cutting off aid or trade to North Korea to avoid heightening the risk of regime collapse.

Just as Beijing does not want war or chaos on its doorstep, it does not want Pyongyang to have access to nuclear weapons, given their proximity. A nuclear North Korea would also raise the stakes for regional powers, likely increasing the US’ military presence in the region and giving both South Korea and Japan reason to pursue nuclear weapons.

Why has North Korea become a source of tension in Sino-US relations?

Under President Donald Trump, the US has become increasingly critical of what they see as China’s limited actions in addressing North Korea’s pursuit of nuclear weapons, particularly after the regime’s ICBM test launches. There has been considerable alarm about Pyongyang’s threats to launch missiles towards Guam, a US territory, as well as the possibility of future missiles that could hit the continental US. As a result, the US has pushed for more sanctions, including secondary measures targeting Chinese companies and individuals that help fund North Korea’s arms and nuclear programmes.

On the other hand, China has been frustrated by what analysts describe as an erratic and insufficient US policy approach towards North Korea. Beijing has bristled at accusations – delivered verbally and via Twitter – that it has not done enough or should shoulder the responsibility to curb North Korean nuclear ambitions. It remains wary of US-South Korean ties, with their joint military exercises and the American-backed terminal high altitude area defence (THAAD) missile system near Seoul as particular flashpoints.

Analysts say the two nations have different priorities on the peninsula: China’s primary concern is North Korean regime stability, whereas the US focus is on Pyongyang’s nuclear capabilities.

What are the different approaches China and the US are advocating for on the peninsula?

China has argued for a “dual suspension” approach to the Korean peninsula, calling on the US and South Korea to end their joint military exercises – which are scheduled for next month – if North Korea suspends its nuclear programme. Beijing has also called periodically for multilateral diplomatic negotiations, hoping to resume the six-party talks with North Korea, Russia, the US, South Korea and Japan.

Meanwhile, the US has pushed for a stronger sanctions regime to pressure North Korea to give up its nuclear programme. But observers say there has been a duplicity of voices from Washington with regards to North Korea, a centrepiece of the Trump administration’s foreign policy. Trump has previously said he will keep “all options on the table”, including military action. But US Secretary of State Rex Tillerson recently signalled an openness to dialogue with Pyongyang, and has praised Kim for not taking any provocative actions since the recent UN sanctions.