SHANGHAI (REUTERS) - China's air quality was markedly worse in the first two months of the year than the same period of 2016 following a series of smog outbreaks in northern China, official data published on Friday (March 24) showed.

China says it is winning its "war on pollution" after strengthening legislation, beefing up its monitoring capabilities and cracking down on hundreds of polluting firms, and it said average air quality improved noticeably in 2016.

Environment Minister Chen Jining urged reporters earlier this month to focus on overall trends, which showed China was making rapid progress in its anti-pollution efforts, even though serious problems remained.

But throughout January this year, high winter coal consumption combined with "unfavourable weather conditions" to create heavy smog build-ups throughout northern China, forcing dozens of cities in the region to issue "red alerts" designed to curb industrial activity and thin traffic.

Data collected from 338 cities in the first two months of the year showed that concentrations of small breathable particles known as PM2.5, a key component of smog, rose 12.7 per cent year on year to 71 micrograms per cubic metre, the Ministry of Environmental Protection said in a notice.

China's cities need to bring PM2.5 readings down to 35 micrograms per cubic metre in order to meet state air quality standards.

Ministry data also showed that average PM2.5 readings in the capital Beijing in January and February reached 95 micrograms per cubic metre, up 69.6 percent from the same period of last year.

Readings in the pollution-prone Beijing-Tianjin-Hebei region as a whole hit an average of 111 micrograms, up 48 per cent compared to the first two months of 2016.

Of the top 10 smoggiest cities, six were in Hebei province in the first two months of the year, with the provincial capital Shijiazhuang ranking the worst, the data showed.

Hebei surrounds Beijing, and it said on Thursday that it would plant trees, establish green belts and make use of rivers and wetlands to create a "green necklace" to protect Beijing from pollution.

Beijing has promised "extraordinary" measures this year to combat smog, while Hebei is aiming to cut coal consumption by households and small-scale enterprises, a major source of smog in the region.