head of Putin's visit, Reuters spoke to analysts about its significance and what to expect.

Graeme Smith, senior fellow at the Australian National University's Pacific Affairs Department, said the optics were striking.

"So there's no doubt that the timing of this visit is a bit cheeky on China's part and on Russia's part. And effectively Trump has been sandwiched because just before he arrived you had the Iranian foreign minister in town and immediately after he leaves he has the Russian leader in town," Smith said.

Kerry Brown, professor of Chinese studies at King's College London, said China would want to "express solidarity" with Russia and also "to make clear that China is a very powerful country and that the people from different places are coming to China to explore options."