Northeastern China, where heavy haze lingered for days, faces a tougher situation in curbing air pollution due to greater pressure on economic growth and a lack of scientific guidance, a survey said on Monday.

Officials from the environmental protection bureaus in northeastern provinces have expressed their urgent need to receive support on air pollution control technology, said Wan Wei, a researcher from Clean Air Asia, a global NGO, which released a survey on air pollution control in China on Monday.

The survey found that many cities in eastern regions such as Shanghai had a clear picture on sources of pollution and drafted targeted control efforts. But provinces in the northeastern region have lagged behind in this respect.

Besides, the region, with heavy industry as its economic pillar, has faced slowing economic growth recently, giving policymakers greater pressure to maintain the pace of development and reluctant to restrict industrial output, which is a major way to reduce air pollution.

In the past week, cities in the region have seen heavy smog. Shenyang, for example, had PM2.5 readings surpassing 1,400 micrograms per cubic meter.