TOKYO — Japan lodged a formal protest with China's embassy against what it called an incursion by a Chinese survey ship into its territorial waters on Saturday, Tokyo's Foreign Ministry said.

The ministry expressed "strong concern" after the ship was spotted near southwestern Kagoshima prefecture early in the morning.

The Chinese ship, which was confirmed to be in territorial waters at 6 a.m. (local time), left shortly before 8 a.m., the ministry said, adding that it was monitored by a Japanese military vessel and plane.

China's increasingly assertive activity around Japanese waters and airspace has caused unease among Japanese defense officials, who are also concerned about the growing military cooperation between the Chinese and Russian air forces.

This follows Tokyo's protest after a Chinese military aircraft briefly entered Japan's southwestern airspace on Monday. It was the first time Japan's Self-Defense Force detected a Chinese military aircraft in the country's airspace.

Chinese Foreign Ministry spokesman Lin Jian said on Tuesday his country had "no intention" to violate any country's airspace.

Bilateral business ties between the two countries, as well as exchanges among scholars and business people among others, remain strong.