TOKYO (AFP) - Beijing's behaviour in its row with Tokyo over disputed islands in the East China Sea is jeopardising peace, Japan's defence minister said on Tuesday.

"I believe the intrusions by China in the territorial waters around the Senkaku islands falls in the 'grey zone' (between) peacetime and an emergency situation," Mr Itsunori Onodera told reporters in Tokyo.

Mr Onodera's comments come days after China's defence ministry said Japan's reported plan to shoot down its drones would constitute "an act of war".

The two sides have been at loggerheads over the island chain, claimed by China as the Diaoyus, since Tokyo bought three of them from their private Japanese owner in September 2012.

But the comments from the two defence ministries appear to have taken the verbal fisticuffs to a new level.