China has warned Japan that it is "playing with fire" in the South China Sea after Tokyo said it would step up engagement in the contested waters.

The rebuke on Thursday comes just days after China sent fighter jets — part of a group of more than 40 aircraft — through a key international entryway into the Western Pacific for the first time, skirting islands in Okinawa in a manner that caused Japan to scramble fighter jets.

On a visit to Washington earlier this month, Defense Minister Tomomi Inada said that Tokyo would "increase its engagement in the South China Sea through ... Maritime Self-Defense Force joint training cruises with the U.S. Navy" and via maritime capacity-building with littoral states in the region.