北京，天津，河北发布烟雾警报

Having just three days of rare clear view and precious blue skyline, north China is once again smothered by a dense grey haze, as if it cannot wait to "catch up" with the east, which is still choking from the heavy smog. Authorities have issued alerts in the cities of Beijing, Tianjin and Hebei Province, and they say they have put emergency plans into effect.

As of 4 p.m. this afternoon, Hebei Province upgraded its pollution warning to red, the highest on the scale. In parts of the province, visibility fell below 50 meters when the PM2.5 index registered a level of 380, which is considered "seriously polluted", prompting authorities to close expressways. Several flights at the airport in the capital city of the province are cancelled.

In the capital, visibility dropped sharply as authorities issued a heavy air pollution warning. Residents have been advised to stay indoors as much as possible. Meanwhile, authorities in Tianjin have said gas emissions from vehicles as the number one source of pollutants.

Temporary relief is expected on Sunday when a cold front arrives and hopefully cleans the air.