China's capital Beijing has launched a month-long campaign to stamp out air pollution violations, the official Xinhua news agency reported on Monday, after the city was choked by two sandstorms in as many weeks.

Beijing's air quality index (AQI) reached the maximum 500 on Sunday, as dust carrying extremely high levels of hazardous particles blew in from Mongolia and northwest China. In mid-March, the city was hit by what China's weather bureau called the biggest sandstorm in a decade.

Although external factors were blamed for the conditions, the Beijing authorities will carry out inspections on all local construction sites until the end of April, severely cracking down on violations such as allowing construction dust to get out and unpunctual clearance of waste, Xinhua said.

Beijing's infamous smoggy skies have cleared up in recent years after China imposed tighter emissions standards on industry in surrounding areas.

So far in 2021, however, the number of air pollution violations investigated and dealt with by Beijing's urban management law-enforcement bureau has increased by 30% year-on-year to 4,791, Xinhua said.

The AQI reading in Beijing was down to 104 as of 1030 GMT on Monday, still classed as "unhealthy".