China and Russia's leaders hailed a "new era" in their relationship on Tuesday, putting on a united front in Moscow as Vladimir Putin accused the West of rejecting Beijing's proposals to end the Ukraine conflict.

The nations, eager to curb Western power, expressed concerns about NATO expansion in Asia and agreed to deepen a partnership which has only grown closer since Putin launched an offensive in Ukraine.

Putin said he was open to talks on Ukraine and praised Beijing's 12-point position paper on the conflict, which includes a call for dialogue and respect for all countries' territorial sovereignty.

He accused Kyiv of not being willing to implement China's proposals, which the United States has said would simply consolidate "Russian conquest" and allow the Kremlin to prepare a fresh offensive.

"Many of the provisions of the peace plan put forward by China... can be taken as the basis for a peaceful settlement when Kyiv and the West will be ready for it," Putin said after talks with Chinese leader Xi Jinping.

"However, so far we have not seen such readiness on their part."

Ukraine's President Volodymyr Zelensky said Kyiv had invited China to talks, and is waiting for an answer from Beijing.

"We offered China to become a partner in the implementation of the peace formula. We passed over our formula across all channels. We invite you to dialogue. We are waiting for your answer," Zelensky told a press conference on Tuesday.

'Unlimited possibilities'

Moscow and Beijing have over the past years ramped up cooperation, both driven by a desire to counterbalance US global dominance.

The Chinese leader's Moscow visit has been viewed as a boost for Putin, who is subject to an International Criminal Court warrant over accusations of unlawfully deporting Ukrainian children.

"I am sure that Russian-Chinese cooperation has truly unlimited possibilities and prospects," Putin said at a state dinner following the talks, where he toasted the "prosperity" of Russian and Chinese people.

He earlier gushed over the "special nature" of the relationship between the two countries in remarks broadcast on state television.

On the second day of his visit to Moscow, Xi said ties with Russia were "entering a new era".

Putin called the talks "meaningful and frank" and said that Russia, which has been largely cut out of European markets because of sanctions, would be able to meet China's "growing demand" for energy.

Energy is a key focus of Xi's visit, and Putin announced the two countries had reached an agreement on the Power of Siberia 2 gas pipeline, which will connect Siberia to northwest China.

US 'undermining' global security

In a joint statement, the two leaders took aim at the West, accusing the United States of "undermining" global security.

"The parties call on the United States to stop undermining international and regional security and global strategic stability in order to secure its unilateral military advantage," Russia and China said in the declaration.

They also expressed "great concern" over NATO's growing presence in Asia.

On Monday, Xi and Putin held four and a half hours of talks, calling each other "dear friend."

China and Russia have often worked in lockstep at the UN Security Council, using their veto power as permanent council members to counter the West.

Russia's assault on Ukraine has also deepened fears among Western powers that China could one day try to take control of the self-ruled island of Taiwan, which Beijing sees as part of its territory.

China has sought to portray itself as a neutral party in the Ukraine conflict, but Washington has said Beijing's moves could be a "stalling tactic" to help Moscow.

US Secretary of State Antony Blinken said Xi's Moscow visit "suggests that China feels no responsibility to hold the president accountable for the atrocities committed in Ukraine".

"And instead of even condemning, it would rather provide diplomatic cover for Russia to continue to commit those great crimes," he added.

The United States has accused Beijing of mulling arms exports to Moscow, claims China has vociferously denied.

Japan PM in Kyiv

Xi's trip coincides with a surprise visit to Kyiv by Japanese Prime Minister Fumio Kishida, who visited Bucha, a town where Russian forces were accused of committing atrocities during their occupation last year.

Ukraine's foreign ministry described the trip as "historic" and called it "a sign of solidarity and strong cooperation between (Ukraine and Japan)".

Kishida, the last Group of Seven leader to visit the country, had come under increasing pressure to make the trip, as Japan hosts the grouping's summit this May.

Zelensky confirmed on Tuesday he would participate in the G7 summit via video link.

Japan and China are close trading partners, but Tokyo has been increasingly worried about Beijing's growing assertiveness in the region.

Japan is part of the US-led security alliance known informally as the Quad, which also includes India and Australia, and positions itself as a bulwark against China's military ambitions in Asia and the Pacific.