Tokyo is worried about China's recent arms buildup but wants to build friendly relations to prevent conflict between the Asian giants, Japan's defense chief said Sunday.

"We are greatly concerned," Defense Chief Fukushiro Nukaga told the television talk show "Sunday Project," citing China's rapid military spending in recent years.

He also said Chinese military vessels have been repeatedly spotted in recent months near disputed waters in the East China Sea.

"We have to be careful and deepen our exchanges [with China] before these things actually turn into military threats," he said, proposing joint defense exercises and defense policy dialogue between the two countries.

Nukaga also urged China to be more transparent in its defense policies.

"Through such efforts we can develop trust, and once we can read what's behind their actions we can have a sense of stability," he said.

China's defense budget has increased by double-digits in recent years amid rapid economic growth. The nation has become one of the biggest purchasers of planes and naval craft from Russia, using high-tech Chinese-made computer and communications equipment.

Earlier this month, a Chinese military vessel approached Kume Island in southern Japan, briefly violating Japan's territorial waters in the East China Sea. But it left the area after warnings from a Japanese coast guard patrol plane.

Japan's Defense Agency also says its fighter jets scrambled 30 times in the past six months to repel Chinese planes in its airspace — more than twice the number in the same period last year.

Tokyo and Beijing have been quarreling over issues including undersea gas deposits, ownership of some islets in the East China Sea and Prime Minister Junichiro Koizumi's visits to a Tokyo shrine that honors war criminals.

Koizumi visited the shrine last month, sending Japan's relations with China to their worst low in decades. Some Asian nations see his visits to the Yasukuni Shrine as a symbol of Japan's ambitions to return to its militarist past.

Koizumi and other Japanese ministers did not meet with Chinese officials during the Asia Pacific Economic Cooperation forum in Busan, South Korea.