As for China, this is a result of the One Child Policy. They are trying to reverse it now because of the aging population but it seems people are not interested in having more children.
The Chinese population is around 1.4 billion, and despite the one-child policy, the population is still growing. Analysts expect the Chinese population to grow until 2030. Without the one-child policy, the situation could have been disastrous.
I don't see any disaster. In China people are not starving. Moreover, the Chinese produce a lot of industrial goods to the world and even export food. Until will continue these trends, the disaster will be.