In many wealthy societies the very old are candidates for nursing home care. That sector is still tiny in China, though, especially compared with the size of elderly population. Zhang Minsheng opened the city's first private nursing home in 1998 in an industrial area far from central Shanghai. It is now 95 percent occupied.

"People were not willing to enter nursing homes in the past, because they were considered places for those without descendants," Mr. Zhang said. "Now, from the standpoint of ordinary people, it is becoming a normal thing."

The average age of the residents of Mr. Zhang's home is 85, and most live several to a room, sleeping on narrow beds separated by flimsy partitions. Many pass the daytime hours in long corridors furnished with chairs, where they chat or simply stare into the distance.

The sheer magnitude of the aging phenomenon has Chinese officials and academics grasping for answers, but almost everyone agrees that there are no easy fixes. Population experts here speak of "patching one hole and exploding another."

China has a wide range of retirement ages, generally from 50 to 60. Raising the retirement age would relieve pressures on the pension system but make it harder for young people to find jobs. And it would be resented by many elderly people, most of whom have missed out on China's economic boom.

Lifting restrictions on internal migration raises the unwelcome prospect of a mass migration, while abandoning the one-child policy would be politically unpalatable.

The government has already tinkered with the policy. It now allows husbands and wives who were their parents' only children to have a second child, for example, and has eliminated a four-year waiting period between births for those eligible to have a second child.

But Chinese demographic experts say the leadership is unlikely to abolish the one-child rule, because it is reluctant to admit that one of its signature policies was in any way a failure - particularly in view of the disastrous population boom encouraged by Mao in the 1950's.

Moreover, lifting child-bearing restrictions might not help. Poorer people in the interior might have more children, but the rising middle class probably will not, experts say.

"More births would only change the structure of the population and prolong the aging process" of the society as a whole, said Ren Yuan, a professor at the Population Research Center of Fudan University in Shanghai. "But it has nothing to do with the number of old people. The scale of this large group has already become a reality. The beds you've got to add in nursing homes, the labor you need to take care of the old, is a reality than can't be changed."