BEIJING - Amid the country's effort to build a greener energy system, the country's raw coal production by its large-size coal companies continued to decline in 2016.

Combined raw coal production from the country's designated large coal companies with annual turnover of at least 20 million yuan (about $2.9 million) stood at 3.36 billion tons in 2016, down 9.4 percent from 2015, latest data from the National Bureau of Statistics (NBS) showed.

Raw coal production from those companies in December 2016 alone was 310 million tons, down 3 percent year on year, said the NBS.

Coal is the main energy source in China, accounting for 64 percent of total energy consumption in 2015.

Cutting overcapacity in sectors including coal and steel is part of the country's supply-side structural reform and high on the government agenda.

The world's largest coal producer and consumer will cut outdated coal capacity by 800 million tons per year by 2020, while increasing use of cleaner coal by 500 million tons each year, according to the coal industry 2016-2020 development plan.