China's state-run media on Friday seized on an apology by former Japanese prime minister Yukio Hatoyama during a visit to a wartime atrocity memorial, amid tense relations between the two countries.

Hatoyama is no longer a member of the Diet, Japan's parliament, and his party is now in opposition, but reports and pictures of his visit to the Nanjing Massacre Memorial were splashed across the front pages of both Chinese and English-language papers.

Relations between the two Asian powers, including the dispute over East China Sea islands claimed by Beijing as Diaoyu but controlled by Tokyo, which calls them Senkaku, are heavily coloured by history.

"I apologise for the crimes that Japanese soldiers committed during wartime," the Global Times quoted Hatoyama as saying.

"As a Japanese I feel responsible for the tragedy and I am here expressing my sincere apology," Chinese web portal Sina reported.

The nationalist Global Times -- which has painted new Japanese prime minister Shinzo Abe's current trip to south-east Asia as an attempt to "encircle China" -- welcomed his comments, and his earlier recognition of a dispute over the islands.

"Hatoyama's words and deeds these days show that in spite of the tough environment, forces which are friendly to China have not disappeared," the paper said in an editorial.

"Besides never giving way to Japan in both the waters and airspace of the Diaoyu Islands, we can find more ways to deal with Japan."

Officially Japan's position is that there is no dispute over the territory, and in Tokyo, Japanese Chief Cabinet Secretary Yoshihide Suga said this week that Hatoyama's comments on the issue were "clearly contradicting our country's stance".

"The remarks made by (former) prime ministers of our country were extremely regrettable," he said.

The row has seen Chinese state-owned vessels entering what Tokyo considers its territorial waters several times, and earlier this week Japanese fighter jets scrambled in response to a Chinese plane flying close to -- but not inside -- the islands' airspace.

Hatoyama was prime minister for just nine months when his left-leaning Democratic Party of Japan ended half a century of almost unbroken rule by the conservative Liberal Democratic Party in 2009.

He is the third former Japanese head of government to visit the Nanjing site.

China says 300,000 civilians and soldiers died in a spree of killing, rape and destruction in the six weeks after the Japanese military entered its then capital on December 13, 1937.

Some Japanese revisionists claim the number of deaths is far lower.