Both sides are boosting their military budgets as they grow increasingly wary of each other's ambitions in the Asia-Pacific region, facing off over a maritime territorial dispute and how to interpret Japan's motivations and actions during World War II.
Japan is uneasy about what it sees as China's growing assertiveness, including through regular double-digit increases in its defence spending, and on Wednesday commissioned its biggest warship since World War II, the helicopter carrier Izumo.
The 248-metre Japanese-built vessel can carry nine helicopters and is aimed at beefing up Tokyo's maritime defences in the East China Sea.
Tokyo has repeatedly called on Beijing to be more transparent about its military outlays but Chinese foreign ministry spokeswoman Hua Chunying hit back, saying that despite Japan's far smaller number of people it spends a hefty amount on defence.
"Japan's population accounts for only about one-tenth that of China," Hua told a regular briefing today.
"But its per capita national defence spending is about five times that of China," she added.
"Given this, Japan's criticism of China's national defence is quite ridiculous."
It was unclear on what figures Hua based her comparison.
Japan's defence spending for fiscal 2015 has been set at 4.98 trillion yen (USD 42.1 billion), or about USD 329 per capita, just over three times as much as China.
Kyodo news agency said the Izumo cost around 120 billion yen.
Beijing is suspicious of moves by Tokyo to increase its defence profile under nationalist Prime Minister Shinzo Abe, who has called for his country to throw off the constraints of its "peace" constitution imposed by the United States after World War II, which ended 70 years ago this year.