Are ninjas Chinese or Japanese

Japanese.

During when Mongolia invaded beijing chinese generals and Lin Kuei (forest ghost) Buddhist monks travelled to the east by boat and landed at Japan.

History tells that a Monks lived in the Mountains of Iga. Later on a samurai met with a monk in the mountain and the monk thought him a new fighting style which called ninjutsu(art of stealth).

The art was passed down secretly since the art was banned by bushido.They dressed like normall farmers or travellers and descised there weapons as farming tools or Musical Instruments. For example the blow gun was descised as a bamboo Flute