The biggest UN summit on sustainable development in a decade approved a strategy to haul more than a billion people out poverty and cure the sickness of the biosphere, AFP reports.

But critics branded the plan a cruel failure, saying it had been gutted of ambition by national interests.

"It's a demonstration of political impotence, of system paralysis, and it makes me feel pessimistic about the system's ability to deliver," Laurence Tubiana, director of a French think-tank, the Institute for Sustainable Development and International Relations (IDDRI), said in an interview.

"The multilateral process today is not delivering the urgent action we need," WWF's Jim Leape told AFP in an email. "International action is in fact important, to galvanize a global response to these challenges, but it's clear that we need to look to leadership in other places... that means looking for changes everywhere - communities, cities, national governments and companies."

The gathering of 191 UN members crowned a 10-day forum marking 20 years since the Rio Earth Summit, where leaders vowed the world would live within its environmental means. In a sprawling 53-page statement, the three-day summit voiced dismay at entrenched poverty and mounting ecological stress.

"We... renew our commitment to sustainable development, and to ensure the promotion of an economically, socially and environmentally sustainable future for our planet and for present and future generations," it said.

Entitled "The Future We Want," the statement highlighted the many perils facing a planet whose human population is set to surge from seven billion today to 9.5 billion by 2050.

The long list includes climate change, desertification, fisheries depletion, pollution and deforestation, and the danger that thousands of species will go the way of the dodo.

"Sustainable Development Goals" will replace the UN's Millennium Development Goals from 2015, although defining the aim will be left for future talks - a process likely to be long and fiercely fought.

The strategy also promotes the green economy, a concept that breaks new ground in official UN terminology but is viewed suspiciously by many developing economies.

The statement also reflected the worries of advanced economies battling a deep financial crisis.

Despite the demands of developing nations for $30 billion in help, the text stipulated no funding figures to achieve sustainability goals.