The incident comes a year after a Japanese mother and child were wounded in a knife attack in the same city. A Chinese woman had died trying to stop the assailant.

In Thursday's attack, "a Japanese national walking with a child was struck by what appeared to be a rock by an unknown assailant inside a Suzhou, Jiangsu Province subway station", Tokyo's embassy in Beijing told AFP in a statement.

A spokesperson for China's foreign ministry told AFP that "the suspect has been apprehended".

The victim was "promptly taken to hospital for treatment, and there is no threat to life", the ministry said.

China and Japan are key trading partners, but increased friction over territorial rivalries and military spending has frayed ties in recent years.

Japan's brutal occupation of parts of China before and during World War II remains a sore point, with Beijing accusing Tokyo of failing to atone for its past.

In June last year, a Japanese mother and child were attacked in Suzhou on the anniversary of the 1931 "Mukden incident", known in China as a day of national humiliation.

The 1931 explosion of a railway in China was used by Japanese soldiers as a pretext to occupy the city of Mukden, now called Shenyang, and invade the wider region of Manchuria.

And in September, a Japanese schoolboy was fatally stabbed in the southern city of Shenzhen.

Media reports about the latest attack in Suzhou were censored on the Chinese messaging app WeChat.

"The Japanese government has urged the Chinese government to... severely punish the suspect, prevent similar incidents, and ensure the safety of Japanese nationals", Tokyo's embassy said Friday.

Beijing's foreign ministry said "China will continue to take effective steps, to protect the safety of foreigners in China".