Tourists in mask visit Wanchun Pavilion in Jingshan Park in Beijing, capital of China, May 4, 2017. [Photo/Xinhua]

The city's meteorological center issued a blue alert for sandstorms Thursday morning, forecasting winds that would carry sand and dust across the capital. Many pedestrians in downtown Beijing were seen wearing protective masks.

Most monitoring stations in the city showed PM10 readings of more than 1,000 micrograms per cubic meter and PM2.5 readings of over 400 micrograms per cubic meter as of Thursday at noon, according to data from Beijing Municipal Environmental Monitoring Center.

Visibility plummeted to as low as one kilometer in many parts of Beijing and is expected to fall further.

According to the Beijing Times, more than 40 flights at Beijing Capital Airport were delayed due to the sandstorm, with another 15 canceled.

Neighboring Tianjin Municipality was also hit by dust and sand, which darkened the sky and effected traffic flow.

"The sky turned gray and the smell of dust and sand had crept into my room this morning. My child complained about feeling uncomfortable after playing outside," said a Tianjin resident surnamed Liu.

Traffic authorities have advised drivers to reduce their speed and to use their fog lights.