Prince William has warned that the future of wildlife is under threat from rapid population growth, as he prepares to welcome his third child.

The Duke of Cambridge, 35, made the comments at the Tusk gala dinner in London on Thursday night, saying: 'In my lifetime, we have seen global wildlife populations decline by over half.

'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.

'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.'

William's father Prince Charles previously spoke out about his concerns over population growth in a 2010 speech at the Oxford Centre for Islamic Studies, warning that the world faces 'monumental' problems as populations rocket.

The Duke of Cambridge, 35, made a passionate speech about his concerns about population growth at the Tusk gala dinner in London last night

Earlier this year an environmental organisation based in San Francisco wrote an open letter to the Cambridges urging them to 'lead by example' by not having any more children

He cautioned that earth doesn't have the capacity to 'sustain us all', while a 'vast proportion' is consuming natural resources at 'Western levels'.

'It would certainly help if the acceleration slowed down, but it would also help if the world reduced its desire to consume,' he said.

In 2008, in an interview for a documentary with Sir Trevor McDonald, the Duke of Edinburgh also issued a warning about overpopulation.

The food prices are going up – everyone thinks it's to do with not enough food, but it's really that demand is too great, too many people."

The Duke adds: "It's a little embarrassing for everybody, no one quite knows how to handle it. Nobody wants their family life to be interfered with by the government."

William is set to become a father-of-three when Kate gives birth in April 2018, but before the news was announced a San Francisco based organisation called on the couple to 'lead by example' and stop at two children for environmental reasons.

In a 2010 speech, Charles warned that rapid population growth means the earth can't sustain all of us. His father The Duke of Edinburgh has also said overpopulation is at the root of many of the world's problems

Having Kids, which promotes smaller families, wrote an open letter to the royal couple in July urging them to 'consider forgoing having a third child (...) in favour of modelling a smaller, sustainable family.'

The organisation spoke out after Kate joked about having more children when presented with a baby gift during the royal tour of Poland.

Having Kids executive director Anne Green said: 'William and Kate have a tremendous opportunity to model their choice of having a smaller family.

'By doing so, they set an example as to what has the most potential for mitigating climate change and its impacts, including severe flooding, deadlier heatwaves, increase in diseases, and wildlife extinctions.'

She added: 'Moreover, given the vast economic inequalities in the world today, the couple also has the opportunity to model a simple principle: That every child deserves as fair start in life'.

William arriving with Tusk CEO Charlie Mayhew at a gala dinner for the Tusk conservation charity at the Roundhouse in London