Intensive military cooperation between China and Russia is set to raise the eyebrows of their wary neighbours.
One of the developments being closely watched is the negotiations between Beijing and Moscow over the sale of the S-400 anti-aircraft missile system. While they have dragged on since 2010, a senior Russian official said progress was made recently.
"The chances that China may be the first foreign buyer [of S-400s] are high," the official Voice of Russia cited the Kremlin's chief of staff, Sergei Ivanov, as saying last month. But he didn't give any additional details.
If the deal is approved, it will be their third big arms deal since last year.
The S-400 Triumph, a new-generation system upgraded from the S-300, which the PLA is using, is capable of countering all air attack weapons, including tactical and strategic aircraft, ballistic missiles and hypersonic targets such as the US' F-35 fighter jet.
With a range of 2,400km, the S-400 can engage up to 36 targets simultaneously with as many as 72 missiles at altitudes of five metres to 30km.
Dr Rajeswari Rajagopalan, a defence analyst at the New Delhi-based Observer Research Foundation think tank, said as India also relied more on Russian arms and military supplies, the S-400 deal between Moscow and Beijing would make India increasingly concerned.
"The Russian insensitivity in selling advanced weapons and platforms to China at the cost of India is a reflection of the new emerging dynamics, and India has to take measures to ensure its own maneuverability while maximising its gains," she said.
"The S-400 deal will not push India to come up with new military strategies, but [will] change geopolitical development and the balance of power in Asia."
Wang Xudong, an adviser on satellites to the central government, said China had other new advanced weapons and missile systems, such as the DF-21D anti-ship ballistic missile, known as a carrier killer, and the DF-41, which is capable of hitting anywhere in the United States.
"China wants to buy the S-400 missile system from Russia because both Beijing and Moscow need to get something from each other," Wang said, adding that Russia needed Chinese funding for research work.
"The S-400 missile system will provide the PLA [with] an alternative weapon, if necessary, and Beijing also doesn't need to spend so much time on producing such a sophisticated armament as tension in the East and South China seas all remind us to be well prepared."
Macau-based military expert Antony Wong Dong said a deal between Russia and China would encourage the US to build closer relationships with the Philippines, Vietnam and even Taiwan.
"It's not clear [how] the military cooperation between Beijing and Moscow will go, but the US would definitely keep a close eye on it, and come up with new strategies," he said.
Wong said the West's decision to punish and isolate Russia in the aftermath of the Ukraine crisis had drawn Moscow closer to Beijing.
"The PLA is expecting to learn some particular missile technologies from the S-400 system. I think China will soon produce a new type of anti-aircraft missile that compares with S-400 because Chinese are [good] copycats," Wong said.
China and Russia are expected to cooperate further on developing the IL-476 transport aircraft and IL-78 airborne refuelling tanker, according to state media in both countries.