Tens of millions of residents in northern China suffered an episode of severe pollution on Tuesday, with authorities calling for a reduction in outdoor activities to escape the gray haze.
In the region around the cities of Beijing and Tianjin and Hebei province, where more than 100 million people live, pollution levels were among the highest in recent months.
In the capital, authorities issued an orange warning on Monday, the second highest for pollution.
Swiss air quality measurement company IQAir on Tuesday ranked Beijing as the world’s fifth-largest city, just ahead of Bombay in India.
According to state agency Chine Nouvelle, residents are asked to “reduce their outings and intense physical activity in the coming days.”
The traffic of certain heavy commercial vehicles and construction machinery is limited.
Authorities have declared a red alert in several areas of the densely populated Hebei province, which surrounds Beijing.
According to an official advisory, the haze reduced visibility to less than 50 meters in the worst-hit locations in the province.
In the city of Tianjin, south of Beijing, home to 15 million people, the National Weather Bureau advised people with breathing problems not to go outside and, if so, to wear a mask.
According to official forecasts, the haze will continue until the end of the week due to “unfavorable weather conditions” expected drop in temperatures in the region.
China officially declared a “war on pollution” in 2014 and air quality has improved significantly in several major cities.
In Beijing, dozens of coal factories were closed and the most polluting industries were moved out of the capital, which had until then been one of the most polluted in the world.
But although progress has been made, air quality is still far from World Health Organization (WHO) standards and China is still the world’s largest emitter of greenhouse gases and considered responsible for climate change.