Prince William says the rapid rise in human population numbers is having devastating consequences for the world.

The Duke of Cambridge, who is expecting his third child with wife Catherine, Duchess of Cambridge, told a Tusk Trust's gala dinner in London that the wildlife is under "enormous pressure" and called for measures to be put in place to minimise the damage caused by the growing population.

The prince's grandfather, the Duke of Edinburgh, advocated "voluntary family limitation" in 2011, to try to solve overpopulation.

"In my lifetime, we have seen global wildlife populations decline by over half," Prince William said at the gala dinner.

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"We are going to have to work much harder, and think much deeper, if we are to ensure that human beings and the other species of animal with which we share this planet can continue to co-exist.

"Africa's rapidly growing human population is predicted to more than double by 2050 - a staggering increase of three and a half million people per month," he added.

"There is no question that this increase puts wildlife and habitat under enormous pressure.

"Urbanisation, infrastructure development, cultivation - all good things in themselves, but they will have a terrible impact unless we begin to plan and to take measures now."

Poor water supplies, overgrazing and illegal animal trading are also to blame, he said.

The trade is particularly "barbaric".

"The world is a worse place for it, and we must stamp it out. "

The UK has recently announced plans to restrict sales of ivory within the country.