Officials of Chinese and international environment agencies Saturday asserted that economic development should no longer be at the cost of environmental degradation.

Achim Steiner, Under Secretary General of the United Nations, said at the Environmental Protection and Urban Responsibilities Forum in Nanjing, that China had achieved extraordinary economic development over the past three decades, but also suffered from great ecological losses.

Steiner, also executive director of the United Nations Environment Programme (UNEP), urged all the countries, including China, to innovate in economic development, especially in the field of urbanization.

"More than half of the world's population lives in cities, and this trend is set to rise by a further 2 billion in the next 25 years. Therefore, cities are where the future of sustainable development will be won or lost," Steiner said.

"Unless a more intelligent development path can be realized, the growth of cities will lead to significant impacts on their hinterlands, given that they already consume more than 75 percent of the world's natural resources. At the same time this is also an opportunity for cities to drive a transition to a low-carbon, resource-efficient green economy."

"On a planet of 6 billion people, rising to over 9 billion by 2050, a fundamental shift and a re-think of stainability will be the key to whether humanity thrives, let alone survives, over the coming decades," Steiner said.

Rajendra Kumar Pachauri, chair of the Intergovernmental Panel on Climate Change (IPCC), said China had done very well in feeding its population, but its industry-led growth came at a cost.

Wearing a green tie, Pachauri, who represented the IPCC , which shared the Nobel Peace Prize with Al Gore in 2007, said a sustainable urbanization mode should be found, and abuse of natural resources should be avoided.

Climate change had become one of the greatest challenges facing humanity and only a low-carbon growth mode could achieve sustainable development, said Pachauri.

Also at the forum, China's Minister of Environmental Protection Zhou Shengxian said China was facing unprecedented pressure from a deteriorating environment.

"The old path of economic growth based on environmental pollution implemented in developed countries over the past 300 years is not feasible in China, and China can not afford the losses brought by this development mode," said Zhou.

He said China should explore a new development path that was more efficient and sustainable, cost less, and caused few carbon emissions.

More than 600 officials and scholars from around the world are participating in the two-day forum, a theme event of the Shanghai World Expo. They will address the topics of international cooperation and policies for climate change, a green economy and innovative production models, the role of the public in building green cities, sustainable buildings, and sustainable lifestyle and consumption patterns.