A city in Henan province regularly hit by smog has seen an improvement in its air quality after a controversial crackdown that included the closure of smoky snack stands and restaurants, officials said.

The Shangqiu government introduced a series of tough measures after the Ministry of Environmental Protection summoned its leaders, along with those from four other heavily polluted cities, on April 28.

According to an official statement, as of Thursday, the city's average concentration of PM2.5 - tiny pollutant particles that can harm human health - had fallen by 3.4 percent month-on-month to 56 micrograms per cubic meter. The average PM10 level was 82 micrograms per cubic meter, down by 19.6 percent month-on-month.

"There has been a significant improvement in the environmental quality" after a citywide campaign and "the blue skies with white clouds, unseen for a long time, are now back", the statement quoted an unnamed official as saying.

The campaign was based on nine measures, including controlling dust, a ban on burning straw and removing from the roads any vehicles that do not meet the national exhaust emissions standard.

However, a move to close polluting restaurants led to complaints online that it had affected residents' lives and had quietened bustling streets.

Zhang Hanxin, 28, said she now finds it hard to buy traditional local foods like steamed bread and cold noodles near her home.

"There are very few snack stalls left nearby," she said. "The street used to be busy and lively, but now it looks very quiet. The blot left by the barbecue stalls is still there. I don't know how long it will be like this."

Zhang Fuyi from the city's publicity department said open roadside markets and outdoor barbecue stands have been cleaned up in the campaign, while restaurants that used coal or did not have the right purification facilities for cooking fumes were ordered to close down until they met the standards.

As of Saturday, most of the restaurants affected had reopened, although the environmental protection bureau had still to complete some inspections, he said, adding that residents can still buy steamed bread in markets that meet the standards.