Emissions per capita went up by 3.4 per cent, to an amount equivalent to six tonnes of carbon dioxide, the data showed, while carbon intensity - measured by emission levels per unit of gross domestic product - remained the same as the previous year.

The major source of the increase was electricity generation, which produced greenhouse gas levels equivalent to 29.6 million tonnes of carbon dioxide, 8 per cent higher than in 2010.

It accounted for 69.3 per cent of the total emissions during 2011.

Greenpeace said the increase was a result of a rise in the use of coal and the decreased use of natural gas by power companies during that year, which was driven by an increase in the price of natural gas.

"The higher emissions levels were despite electricity consumption in Hong Kong remaining rather stable in that year," said Yeung Man-yau, a campaigner for the environmental group.

"It might be a consequence of the use of more coal and less use of natural gas, especially by China Light and Power, because depletion of the Yacheng gas field drove up natural gas prices."

The government is currently conducting a three-month public consultation exercise on the city's energy mix which is due to end on June 19.

The two options put forward - importing about 30 per cent of the city's electricity needs from the China Southern Power Grid company in Guangzhou, or a heavier reliance on local energy production via natural gas - could both help reduce carbon emissions, Yeung said.

The second-largest source of greenhouse gas was transport, contributing 17.2 per cent of total emissions, followed by waste (5.3 per cent), other end-use of fuel (4.9 per cent), industrial processes (3.2 per cent) and agriculture, forestry and other land use (0.1 per cent).

At present the local power market is limited to two firms - CLP Power and HK Electric. The regulatory regime expires in 2018 and the government has to inform the two companies by 2016 if it intends to open the market.