Image caption The UN says we should celebrate the rise in life expectancy and falls in infant mortality

A major United Nations report has set out the challenges facing humanity a few days before the world's population is expected to reach seven billion.

The report calls for a change of focus, no longer asking "are we too many", and instead concentrate on making the world better.

It identifies many reasons to celebrate, including increased life expectancy and falling fertility rates.

But it also acknowledges the risks of rapid population growth.

The UN estimates that the world's seven billionth person will be born on 31 October and says by the end of this century, the world's total population could number more than 10 billion.

The report, State of World Population 2011, says this is not a time of crisis but a moment for action.

"The world's population is going to continue to grow and we may as well be prepared for it, " says the editor, Richard Kollodge.

"We may as well make sure that as many people as possible are healthy, that as many people as possible have access to education."

"We have a chance right now in our world of seven billion to build a more stable, more socially just world by the time we reach 10 billion but that requires us to act now," he says.

Image caption The UN says carefully planning will be needed if our cities are to cope with rapid population growth

Reasons to celebrate

The report says the rise in average life expectancy - which has increased from 48 years in the 1950s to about 68 now - should be celebrated.

It says in the same period the fertility rate, which is the average number of children women have, has dropped by more than half, from 6.0 to 2.5.

It also notes that children are much less likely to die in infancy thanks to improvements in health care.

The challenges from the growth in population include the massive inequalities between different countries in access to food, water, housing and work.

World population in numbers 1 billion- 1804

2 billion- 1927

3 billion- 1959

4 billion- 1974

5 billion- 1987

6 billion- 1999

7 billion- 2011 Source: UN

The report says predicted water shortages need to be addressed now, and better urban planning is needed as cities continue to grow.

It points out that more than 200 million women still have no access to family planning advice and calls for better reproductive education for young women.

"Sex education has an impact in delaying the age at the first sexual intercourse, in increasing the use of contraception methods and condoms," says Gabriela Rivera from the Mexico City offices of the UN's population agency.

Caring for the increasing number of elderly people will also present many challenges, says the report.

The UN has expressed concern that in many poor countries, such as in sub-Saharan Africa, the speed of population growth could hold back economic development and trap future generations in poverty and hunger.