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Andy Wong, Associated Press
A North Korean national flag is seen on a building along the river bank of the North Korean town of Sinuiju, opposite side to the Chinese border city of Dandong, Tuesday, Dec. 20, 2011. North Korea's leader Kim Jong Il died Saturday of a massive heart attack brought about by overwork and stress, according to the North's media.

BEIJING — Chinese President Hu Jintao visited North Korea's embassy in Beijing on Tuesday to offer his condolences on the death of Kim Jong Il as China moved swiftly to assure its communist ally of its strong support amid an uncertain leadership transition.

Surrounded by scores of security officers, Hu made an early morning trip to the sprawling complex in eastern Beijing's leafy Jianguomenwai diplomatic district, where the North Korean flag was flying at half-staff. The official Xinhua News Agency reported the visit but offered no other details.

The visit followed a meeting Monday evening between the embassy's second highest-ranking official and Chinese Foreign Minister Yang Jiechi, who called Kim a "close friend" who would be remembered forever by the Chinese people. On Monday, the ruling Communist Party's Central Committee, China's top policy-setting body, hailed Kim's son and successor Kim Jong Un as North Korea's new leader.

In the Chinese border city of Dandong, visitors delivered flower arrangements Tuesday to the customs office but all appeared normal otherwise. Tourist boats on the Yalu River cruised along the North Korean bank and trucks rumbled across the rickety bridge connecting the sides.

Dandong is the main crossing point for travelers and goods between the countries and a nearby island was designated earlier this year as the site of an experimental cross-border joint economic development zone.

China's response to Kim's death highlights the government's growing emphasis on North Korea ties despite their annoyance at the North's refusal to reform its listless economy and its recurring provocative acts against South Korea that whip up tensions in the region.

Beijing sees North Korea as a strategic bulwark against a democratic South Korea allied with the U.S. In recent years it has become North Korea's indispensable diplomatic protector and economic partner, accounting for the bulk of its trade, much of its investment and all of its oil. Kim was a frequent visitor to China, coming twice this year alone, most recently in August when he stopped off while returning home from Russia.

Chinese experts say that they don't anticipate any change in relations but that Beijing will likely beef up security to guard against disorder that could potentially send millions of impoverished, starving refugees across their long border.

Above all, China wants to preserve the North Korean regime and ensure stability on the Korean Peninsula, while hoping also for economic reforms that will make the North less reliant on Chinese help.

Yet, while officials exude confidence in public, government-backed scholars are far less sanguine, warning that Pyongyang is ill-prepared for a sudden change in leadership to the young and inexperienced Kim Jong Un.

"The situation now is very uncertain and we can't rule out the possibility of greater turbulence in North Korea's internal situation and foreign relations," said Shi Yinhong, an international relations expert at Beijing's Renmin University.