In the Beijing-Tianjin-Hebei region, average concentrations of small breathable particles known as PM2.5 rose nearly 20 percent year-on-year to 85 micrograms per cubic meter from January to April, said the Ministry of Environmental Protection.
China has launched campaigns aimed at ensuring the region meets a series of politically significant 2017 air pollution targets set by the central government in 2013.
The region is under pressure to cut 2012 levels of small particulate matter by around 25 percent by the end of this year, with Beijing aiming to keep average PM2.5 rates at below 60 micrograms per cubic metre, down from 73 micrograms in 2016.
Beijing's average PM2.5 reading stood at 76 micrograms in the first four months of 2017, up 11.8 percent from the same period of 2016.
Chinese cities need to cut average PM2.5 readings to 35 micrograms in order to meet state standards, while the World Health Organization recommends concentrations of no more than 10 micrograms.