Beijing emerged as an economic lifeline for Moscow last year, especially through energy purchases, after Western sanctions over Russia's invasion of Ukraine cut off crucial trade links.
Moscow is confident that the new pipeline -- Power of Siberia 2 -- is going ahead, but Beijing has so far avoided an explicit commitment.
Analysts say the lagging response shows an imbalance favouring Beijing in energy deals between the two countries -- as well as China's wariness of over-reliance on Russia for fuel.
China is "in no rush to sign anything unless the proposal is favourable and is shaped on China's terms," researcher Maria Shagina at the International Institute for Strategic Studies (IISS) in Berlin told AFP.
The project was discussed during Chinese President Xi Jinping's summit with Russian leader Vladimir Putin in Moscow this week.
Putin said after talks with Xi that "all agreements have been reached" on the Power of Siberia 2 project.
But their joint statement only said the two sides will work on pushing forward "research and consultation" on the pipeline.
The Chinese foreign ministry did not respond to a request for more details.
Power of Siberia 2 could facilitate the transport of 50 billion cubic metres of gas to China annually, roughly on par with the total capacity of the controversial Nord Stream 2 pipeline from Russia to Germany.
A senior Russian official suggested last year that it could strategically replace Nord Stream 2.
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