Changchun, China ? Mystery surrounded North Korean dictator Kim Jong Il on his strangely timed visit to China while former U.S. President Jimmy Carter was in North Korea winning the release of an imprisoned American.

Kim’s Thursday trip to China was his second in three months — unusual for a man who never flies and travels only by armored train. It has not been announced by either country.

That has led to speculation by South Korean media and regional analysts that he may be seeking Chinese aid following flooding in his impoverished country’s northwest — and could be laying the diplomatic ground work for the succession of his son, who is thought to be traveling with him.

A convoy of 30 cars left the northeastern city of Jilin this morning where Kim apparently spent the night, South Korea’s Yonhap news agency reported, and was seen entering a government guesthouse in Changchun, an hour’s drive away. The highway between the cities was blocked briefly and an increase in security was seen around the guesthouse.