Rouhani is set to attend the two-day summit of the Shanghai Cooperation Organisation (SCO), a regional security bloc led by China and Russia, which begins Saturday.

Footage from state-run broadcaster CGTN showed the leader smiling broadly as he descended from his plane, striding past a bayonet-wielding honour guard to accept a bouquet of flowers from a young Chinese boy.

The summit comes after US President Trump controversially pulled Washington out of a 2015 international pact with Iran that placed limits on its nuclear programme in return for easing economic sanctions.

Rouhani's presence marks just the second time that an Iranian leader has participated in the annual gathering, now in its 18th iteration.

This year, Iran stands to gain a lot because it "is currently evaluating the signatories of the nuclear deal to see to what extent they'll be able to effectively maintain it even after the US's withdrawal", according to Gao Shangtao, an expert on Middle East relations at Beijing Foreign Affairs College.

The security bloc will also likely mull over whether to allow Iran to ascend from its position as an SCO observer to become a full member state -- a development it has sought since 2008 but has been unable to achieve while subject to UN sanctions.

The 2015 nuclear deal lifted that barrier.

Rouhani is set to meet Chinese President Xi Jinping on the sidelines of the summit, although the nuclear deal and the issue of its membership are not part of the official agenda.

Chinese businesses are expected to step up activities in Iran to fill the void left by the exit of US companies and the possible withdrawal of European rivals who fear punitive US measures.