While North Korea is often a topic when Chinese and South Korean leaders meet, the death of its leader last month has pushed it to the center of the summit, which was to have focused on mending frayed relations over Chinese fishing fleet incursions in South Korean waters and Beijing's support for Pyongyang.

After a pomp-filled welcome at the Great Hall of the People, South Korean President Lee Myung-bak held talks with President Hu Jintao. Lee was to meet with other leaders during his stay.

Beijing is expected to offer to open talks on a three-way free trade agreement with Japan, Chinese state media reported, highlighting the robust economic ties China and South Korea share in contrast with the strains on other fronts.

The presidents are expected to emphasize their shared concern for the stability of North Korea — poor but with nuclear weapons programs — as it makes an uncertain transition to rule by Kim's son, Kim Jong Un, and a coterie of his father's advisers.

"Peace and stability on the Korean peninsula serve the common interests of all parties," Chinese Foreign Ministry spokesman Liu Weimin said about the Lee-Hu summit at a daily media briefing. The sentiment was echoed in a nearly identical statement from the presidential Blue House in Seoul.

Beyond that, however, priorities diverge. China dislikes even talking in detail about its North Korea ally with other countries, seeing it as an invitation to meddling.

"The Chinese will offer little information about North Korea and will only ask that everyone else leave North Korea alone and manage their shaky power transition," said Victor Cha, a Korea expert and former National Security Council official in the administration of President George W. Bush.

Differences between Beijing and Seoul were on display soon after Kim Jong Il's death. The Chinese leadership immediately sent messages of support to the younger Kim, and Hu and other top leaders paid condolence visits to the North Korean Embassy in Beijing. South Korea's Lee put his military on high alert, and while expressing a wish for better relations he vowed a stern reaction to any provocation.

While Beijing, which already accounts for the bulk of North Korea's trade and investment, wants to see an acceleration of economic reforms, it also wants to ensure that Pyongyang's current rulers remain in power. A North Korean meltdown, in Beijing's eyes, would send refugees into China and pave the way for a unified Korea under Seoul, with its strong alliance to the US.