Beijing's air quality reached dangerous levels yesterday after its first sandstorm of the year.

Residents said the sky turned yellow and visibility was poor.

Women, some wearing face masks, struggle through strong winds after Beijing was hit by its first sandstorm of the year on Thursday. [Photo/Shanghai Daily]

Officials advised against going outdoors and said protective measures were necessary for anyone venturing outside.

PM10 readings reached as high as 1,000 micrograms per cubic meter - severely polluted - at 11am but started to drop in the afternoon, according to data from the capital's environmental monitoring center.

PM2.5, smaller particles which are particularly dangerous as they can lodge in the respiratory system, reached 500 at 11am in many parts of the city.

The national safe air limit is an average of 75 micrograms of PM2.5 per cubic meter within 24 hours.

Beijing suffered 16 days of haze in January, the most since 1954.

The city usually suffers sandstorms from late February to mid-April and the monitoring center said residents should be prepared for a repeat of yesterday's conditions on March 9 and 10.

In neighboring Tianjin, dense smog forced the city's meteorological observatory to issue two alerts since Wednesday.

Statistics from the Tianjin Environmental Bureau showed that PM2.5 readings at seven of the 27 monitoring stations across the city exceeded 300 yesterday.

Sections of 15 expressways passing through Tianjin had to be closed temporarily.