China, the United States and Qatar were accused of environmental plunder on Tuesday as green activists marked "Earth Overshoot Day," the date at which mankind has exhausted a year's budget of natural resources.

"In just over eight months, we have used as much nature as our planet can regenerate this year," Global Footprint Network, an international thinktank which calculates the metric, said in a press release.

"The rest of the year corresponds to overshoot. We will maintain our ecological deficit by depleting oceans of fish, trees and other resources, and accumulating waste such as carbon dioxide in the atmosphere."

It would take more than one and a half Earths to meet humanity's present rate of consumption, the group said, adding: "We are on track to require the resources of two Earths well before mid-century."

In its appraisal for 2012, Global Footprint Network said more than 80 percent of the world's seven billion people -- due to rise to more than nine billion by 2050 -- live in countries that devour more resources than their ecosystems can renew.

China's total ecological footprint is smaller, per capita, than in Europe or North America.

But, the organisation pointed out, China's footprint is the heaviest in the world in raw size, simply because of its huge population.

If the world's population adopted the lifestyle of a typical resident of China, it would take 1.2 Earths, it said.

"Other countries' per capita demands on the planet's ecosystems are even higher: if everybody were to live like United States residents today, it would take four Earths to support the global population," the report said.

"In Qatar, the typical resident requires the resources of six and a half Earths."

Global Footprint Network says that, according to its latest crunching of the numbers, Earth first lurched into ecological debt on December 29 1970.

In 2012, "Earth Overshoot Day" was designated for August 22, but new calculations suggest that a more accurate date was August 23, it says.