Mr Kim, whose rare foreign trips are cloaked in secrecy, arrived late in the evening at Yangzhou railway station, reported the Yonhap news agency and YTN television network, both citing unidentified sources in the city west of Shanghai.
Meeting in Japan, Chinese premier Wen Jiabao told South Korean president Lee Myung-bak that Beijing invited Mr Kim to study China's economic reforms, Mr Lee's office said.
"We invited (Mr Kim] to give (the North Koreans] a chance to understand the Chinese development and use it for their own development," Mr Wen was quoted as saying. Mr Kim's visits to China are seen as a means to shore up support for his faltering economy. North Korea in January appealed for urgent food aid and faces international pressure to end its nuclear weapons programme.
China and North Korea want to resume the six-nation talks on the North's nuclear programme, while fellow participants South Korea and the United States say the North must first exhibit sincerity toward disarmament.
US officials plan to visit the North tomorrow to evaluate its food needs. The UN says six million people - a quarter of the North's population - need emergency help after bad weather hit crops.
China has confirmed Mr Kim's most recent official visits - in last May and August - only after he returned home.