A Japanese daily says North Korean leader Kim Jong-il since April has often passed out while working and been in critical condition.

Quoting a Chinese official well versed in North Korean affairs, the Mainichi Shimbun said Sunday that Kim often works late night and early mornings but could not in May and June because his illness worsened.

The report also said Kim is losing his sense of judgement and Pyongyang's failure to show flexibility at the six-way nuclear talks is also related to his illness.

From April, Kim concentrated on receiving treatment and cut back on work for two months to prepare for a visit by China's Vice President Xi Jinping.

The Chinese official said several of Kim's organs including his kidneys and heart began to show signs of failure from summer of last year, and his illness has since aggravated.