Chinese experts on Korean affairs say they are not sure about the purported illness of North Korean leader Kim Jong-il and also said the rumor is quite strange.

A researcher at the China Institute of International Studies said it's clearly unusual that Kim was absent from the ceremony marking the 60th year of the nation's founding. But he said more time is needed to observe the situation and figure out the reason.

A Tsinghua University professor said if Kim is really ill, it implies a huge change in Northeast Asian dynamics and urged joint measures by the six-way nuclear dialogue parties and neighboring states.

But a professor of Korean studies at Peking University warned against premature forecasts given North Korea's unpredictable behavior. The professor predicted the rumor would be confirmed in a day or two.