Chinese Ambassador to Japan Cheng Yonghua said Sunday that he is optimistic for the future of China-Japan relations, despite the lingering tension between the two nations.

Cheng admitted that his mission as the ambassador is "complicated, sensitive and difficult" at present.

"However, I remain optimistic that generally the two countries will maintain friendly relations in the future," he told Xinhua in an exclusive interview.

"What the two countries need to do now is to improve crisis control and avoid accidents getting out of hand," said Cheng, who is in Beijing for the annual session of the 12th National Committee of the Chinese People's Political Consultative Conference, the country's top political advisory body.

He said the disputes over the Diaoyu Islands, which were triggered by Japan last year and have not been well handled by Prime Minister Shinzo Abe's administration, "is the biggest challenge in improving China-Japan relations."

The Japanese government ignored the history of the islands, the common understanding reached 40 years ago by leaders of the two countries, as well as calls among Japanese people for improving bilateral ties, he said.

Japan must show its sincerity and work with China in finding out an effective way to put the Diaoyu Islands problem under control and solve it at last, he said.

"As the saying goes, whoever started the trouble should end it," the ambassador said.

As the world's second- and third-largest economies, both China and Japan will be hurt if they fight each other, but benefit if they maintain peace, he said.

Since September when the tensions first broke out, the number of tourists across the border has dropped 30 percent and those traveling on package tours reduced by more than 70 percent, he said.