Nigerian president Obasanjo has encouraged voluntary donation

On World Blood Donor Day, the WHO praised the people who regularly and voluntarily donate for no reward.

Thousands of lives are saved every day, it said. But higher donor rates and better co-ordination could make a much greater impact.

"Safe blood is a fundamental need for the health system of any country," said Dr Lee Jong-wook of the WHO.

The accessibility of blood varies widely across the world, says the BBC's Imogen Foulkes.

In wealthy countries 10% of people entering hospital need blood.

Four-and-a-half million Americans would die each year without a transfusion, our correspondent says.

In Britain, it is estimated blood donors saved or improved a million lives last year alone.

Even these countries need improvements, says our correspondent. Britain would have enough supplies for only four days if donors stopped giving.

HIV risk

But in developing countries the need is much greater, says the WHO, calling for more donors and for countries to co-ordinated blood donation systems.

Crucially, blood donation should always be voluntary and unpaid, the WHO says.

This increases safety, as people who volunteer knowing there will be no reward are likely to have a sense of responsibility towards their community.

The WHO says Malawi is a prime example. It set up a functioning national blood service with voluntary donations in just two years.

Since then one major hospital in Blantyre has seen death rates for children with severe anaemia due to malaria fall by 60%.

Maternal mortality is down 50%.

The WHO says that donation safety needs to be improved, as HIV-contaminated blood still accounts for approximately 5% of HIV infections in Africa.

Many poor nations do not test for diseases such as HIV or hepatitis B and C.

But with only 40 countries having established a 100% voluntary blood donation system, the WHO hopes the success of countries like Malawi will be an example to follow and will inspire a new generation of blood donors, says our correspondent.