Chinese President Xi Jinping met his Russian counterpart Vladimir Putin in Moscow on Monday, in what Beijing called a visit of “peace and friendship”.
Mr Putin said he was open to discussing China's peace plan for Ukraine, after Mr Xi arrived at the Kremlin in his first visit to Russia in four years.
The trip serves as a show of support for Mr Putin, who has been isolated internationally.
Mr Xi described China and Russia as “good neighbours and reliable partners” whose talks would “give a new impetus” to their partnership, Russian state media said.
The visit is a political boost for the Russian President after the International Criminal Court issued an arrest warrant for him over accusations of war crimes in Ukraine.
Mr Xi's visit to Russia to discuss economic, political and security ties is expected to last three days.
During his initial meeting with Mr Putin, Mr Xi hailed China's “close ties” with Russia.
Mr Putin said the two countries had “plenty of common objectives and tasks”.
State news agency RIA Novosti said talks between the Russian and Chinese leaders lasted four and a half hours.
The two will meet again for formal talks on Tuesday.
China's Foreign Ministry described Mr Xi's trip as a “journey of friendship, co-operation and peace”.
China has positioned itself as a mediator in Ukraine conflict.
“We are always open to negotiations,” Mr Putin told Mr Xi at the Kremlin. “We will certainly discuss all these issues, including your initiatives, which we treat with respect, of course.”
Kremlin spokesman Dmitry Peskov said Mr Putin had “comprehensive explanations” for the Chinese leader as the war continues after 13 months of fighting.
The Russian President accused western powers of seeking to impose their will on Europe and Asia, to “contain our countries' development and harm their interests”.
Vladimir Putin and Xi Jinping meet in Moscow — in pictures
Mr Xi, in turn, wrote in a signed article carried by Russian and Chinese media that he looked forward to “working with President Putin to jointly adopt a new vision” for relations.
Ukraine said it was closely monitoring the visit.
Oleksiy Danilov, the secretary of Ukraine's national security and defence council, said the heart of any peace plan should be a Russian withdrawal from Ukraine's territory.
Russia last year announced the annexation of four Ukrainian regions after referendums that western powers dismissed as a sham. The Kremlin said Mr Putin visited Mariupol, one of the occupied areas, after dark on Saturday.
Mr Xi is the first world leader to meet Mr Putin since the ICC issued an arrest warrant for the Russian leader on Friday over the deportation of Ukrainian children to Russia since the start of the war.
The US said Mr Xi's visit suggested China did not think Russia should be held accountable, with Secretary of State Antony Blinken saying the world should not be fooled by any tactical moves by Russia, supported by China.
Russia, which rejected the ICC charge, on Monday announced it was retaliating with its own criminal case against the court's prosecutor and judges.
It accused them of making false accusations and preparing “an attack on a representative of a foreign state”.
Former Russian president Dmitry Medvedev said that the ICC's intervention would have “monstrous consequences” for international law.
It is Mr Xi's first foreign trip since he secured a third term as China's President this month.