Greece's government Wednesday ruled out reducing a tax on heating oil despite a sharp increase in smog resulting from extensive wood-burning.

"Reducing the price is not the solution (to the smog problem)," Finance Minister Yannis Stournaras told a joint Christmas Day press conference with Health Minister Adonis Georgiadis and Environment Minister Yiannis Maniatis.

Crisis-hit Greeks are increasingly shunning fuel for cheaper firewood to heat their homes, as energy prices have soared because of tax hikes that are part of the country's EU-IMF bailout deals.

Excessive wood-burning has caused choked skies in Athens and other main cities around the country, prompting repeated pollution warnings.

At the weekend in Athens' northern suburbs, particulate matter was double the normal level for the area, approaching what is considered the alarm threshold of 150 milligrammes per cubic metre.

The three ministers further urged the public to take advantage of heating oil subsidies and free electricity available to low-income families.

On Monday, the health ministry finalised a plan offering free power to poorer households when smog exceeds safety levels.

Under the plan, those registered with the state power company's low-income rates are entitled to two days of free electricity for every day that smog hits the alarm level.

The smog contains sulphur dioxide, carbon monoxide and other carcinogens, all dangerous for public health.

The economic crisis that has stalked Greece since 2010 initially caused pollution to dip because of a drop in automobile traffic.