Traffic police suspended operations on several sections of the major expressway system linking Hanoi with Ninh Binh and Thanh Hoa provinces during the early hours of the day.
From around 5:00 a.m., dense fog enveloped the Cao Bo – Mai Son – National Highway 45 – Nghi Son route, severely reducing visibility and creating dangerous driving conditions.
This marks the first time Vietnamese police suspended expressway traffic due to adverse weather, according to a representative from the Traffic Police Department under the Ministry of Public Security. The closure order remained in effect until visibility improved to safe levels.
Authorities urged drivers to monitor traffic diversion updates and seek alternative routes. For those encountering dense fog, officials advised limiting travel, utilizing fog lights and low-beam headlights, and strictly avoiding lane changes or overtaking.
Dense smog blankets the Cao Bo-Mai Son expressway section passing through Ninh Binh Province, northern Vietnam, Feb. 4, 2026. Video by traffic police.
Hanoi air quality plummets
Coinciding with the heavy fog, air quality in the capital deteriorated rapidly as a cold air mass weakened, trapping pollutants near the ground.
By 8:00 a.m., the monitoring station at the Hanoi University of Science and Technology on Giai Phong Street recorded an Air Quality Index (AQI) of 232.
This falls into the “very unhealthy” category, indicating serious health risks for human. The AQI at this location had been rising since Monday, exceeding the 200 threshold from Tuesday midnight and continued to stay at that level on Wednesday morning.
Other monitoring stations across the region reported similarly alarming figures, including Thai Nguyen (192), Hai Duong (182), Bac Giang (164), and Hung Yen (153).
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Air pollution on Phan Trong Tue Street, Thanh Tri Commune, Hanoi. Photo by Read/Hoang Giang |
Global air quality monitor IQAir ranked Hanoi among the world’s most polluted cities on Wednesday morning with an AQI of 203 as of 10:30 a.m., trailing only Delhi, Lahore, and Dhaka.
Inner-city districts including Tay Ho, Hoang Quoc Viet, and Hoan Kiem all recorded very unhealthy pollution levels.
According to environmental authorities, the spike in pollution is driven by the accumulation of fine particulate matter (PM2.5) under poor atmospheric dispersion conditions. Air quality in Hanoi and neighboring provinces is forecast to remain at “poor” to “very unhealthy” levels throughout the day before potentially easing slightly on Thursday.
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