The amount of energy consumed for every unit of economic output fell 4 percent last year from its 2009 level, according to calculations by the National Bureau of Statistics released on Monday.

Between 2006 and 2010, the country achieved a 19.1-percent drop in energy intensity, roughly meeting its five-year target to improve energy efficiency by 20 percent, Premier Wen Jiabao said on Sunday during an online conversation with netizens.

Wen also unveiled new goals to bring down both energy consumption and carbon dioxide emissions per unit of GDP by 16 to 17 percent from 2011 to the end of 2015.

The targets are still subject to approval from the annual session of the National People's Congress, the country's top legislature, which meets this week.

This is the first time that China has included a mandatory carbon intensity target in its social development programs. Wen said meeting the goals would need "solid efforts."

But some experts expressed concern about the lowered energy targets, fearing they might be too weak to rein in the blind pursuit of economic expansion by local governments.

A study by the World Wildlife Fund's (WWF) climate research team recommended a 20 percent reduction in energy intensity during next five years - the same target as was in the 11th Five-Year Plan (2006-2010) period. The WWF said the target would guide economic restructuring and ensure energy security for the country.

Yang Fuqiang, who led the study, said the 16-percent reduction target may offer an easy ride to local governments who will not need to pay too much attention to controlling their energy consumption.

"Provinces always beat the economic growth target set by the central government, only a stricter energy intensity target would curb the irrational investment," he said.

Although China's growth target was set at 7.5 percent from 2006 to 2010, the country's economy still grew at an annual rate of around 10 percent.

That resulted in a rapid increase in the country's total energy consumption, which also threatened the country's energy security, Yang said.

Last year, China used 3.25 billion tons of standard coal equivalent, up 5.9 percent from the year before, according to the National Bureau of Statistics.

The National Energy Administration said in October that China could limit its total energy consumption to an equivalent of 4.2 billion tons of standard coal in 2015. However, the actual figure may reach 5.1 billion if the current situation remains unchanged, according to a report released on Monday by the Chinese Academy of Engineering.

During the online conversation, Wen also set a lowered annual economic growth target of 7 percent during the next five years, adding that the country should no longer sacrifice the environment for unsustainable economic growth.

In 2009, China announced its goal to bring down carbon intensity by 40 to 45 percent by 2020 from the 2005 level.