TOKYO -- Japanese Self-Defense Forces' aircraft seriously threatened the safety of a Chinese plane that flew normally in the China's Air Defense Identification Zone over the East China Sea, said Chinese Ambassador to Japan Cheng Yonghua Thursday.

Cheng made the remarks when he met with Japanese vice Foreign Minister Akitaka Saiki the day and refuted protest lodged by the Japanese side over what it called "plane encounter" incident.

Special: China's air defense identification zone

Cheng said that Japan's YS11EB and OP3C aircraft tailed after China's Tu-154 plane as close as 30 meters over the East China Sea at around 10 a.m. Wednesday and the Japanese fighters' action seriously threatened the safety of China's plane.

In an effort to prevent further contingency, two Chinese fighters, following orders, flew to the incident airspace and conducted surveillance on the two Japanese planes with a distance of 150 and 200 meters respectively, Cheng said.

Cheng said the emergency situation over the East China Sea was a result of the Japanese airplanes'dangerous move and China resolutely opposes and lodges strong protest against Japan, which ignored the facts and used the incident to play up "China threat."

Cheng also urged Japan to take measures so as to prevent such dangerous incident.