The Shanghai Cooperation Organization (SCO) touts itself as a non-Western style of collaboration between 10 countries in the region and seeks to be an alternative to traditional alliances.
Xi told leaders including Belarusian President Alexander Lukashenko and India's Prime Minister Narendra Modi that the global situation was becoming more "chaotic and intertwined."
The Chinese leader also slammed "bullying behavior" from certain countries — a veiled reference to the United States.
"The security and development tasks facing member states have become even more challenging," he said in his address in the northern port city of Tianjin.
"With the world undergoing turbulence and transformation, we must continue to follow the Shanghai spirit...and better perform the functions of the organization."
Putin used his speech to defend Russia's war on Ukraine, blaming the West for triggering the three-and-a-half year conflict that has killed tens of thousands and devastated much of eastern Ukraine.
"This crisis wasn't triggered by Russia's attack on Ukraine, but was a result of a coup in Ukraine, which was supported and provoked by the West," Putin said.
Ukraine's Foreign Ministry urged China to work towards peace during Putin's visit, saying in a statement from Kyiv they "would welcome a more active role" for Beijing to help find peace "based on respect for the UN Charter."
Putin meanwhile praised Turkey's mediation efforts in the conflict as he met Turkish counterpart Recep Tayyip Erdoğan.
And Putin later met his Iranian counterpart Masoud Pezeshkian, the Kremlin said, with the pair expected to discuss Iran's nuclear program.
'Always insightful'
Earlier, leaders from the 10 countries — China, India, Russia, Pakistan, Iran, Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan and Belarus — posed for a group photo on a red carpet.
Xi, Putin and Modi were seen chatting, flanked by their translators. Modi and Putin were photographed holding hands and held talks in the afternoon.
Russian state media reported the pair spent nearly an hour talking "face-to-face" in Putin's armored presidential car before an official meeting.
"Conversations with him are always insightful," Modi posted on X alongside a photograph of them traveling in the car.
Before their meeting, Modi praised the "special and privileged strategic partnership" with Moscow and added that India wanted both sides in the Ukraine conflict to "find stable peace."
'Mutual trust'
The SCO summit kicked off on Sunday, days before a massive military parade in Beijing to mark 80 years since the end of World War II.
The member states signed a declaration Monday agreeing to strengthen cooperation in sectors such as security and economy, China's Xinhua news agency said.
Xinhua added that the leaders also admitted Laos as an observer country, or "dialogue partner" — the summit already has 16 observers.
Xi held a flurry of back-to-back meetings with leaders including Lukashenko — one of Putin's staunch allies — and Modi, who is on his first visit to China since 2018.
Modi told Xi that India was committed to taking "forward our ties on the basis of mutual trust, dignity and sensitivity."
The world's two most populous nations are intense rivals, competing for influence across South Asia and having fought a deadly border clash in 2020.
A thaw began last October, when Modi met Xi for the first time in five years at a summit in Russia.
Their rapprochement deepened as U.S. President Donald Trump pressured both Asian economic giants with trade tariffs.
More than 20 leaders are attending the bloc's largest meeting since it was founded in 2001.
Many of the assembled dignitaries will be in Beijing on Wednesday to watch the military parade, which will also be attended by North Korean leader Kim Jong Un.
Kim left Pyongyang by train on Monday afternoon and is expected to arrive Tuesday, South Korea's Yonhap news agency reported.
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