China issued dangerous heavy fog warnings for many regions and shipping was suspended in the Qiongzhou Strait, an important economic transport hub near Hainan, according to state and local media on Tuesday.

Video footage and pictures from social and local media showed thick fog in several cities with visibility of less than seven metres in some areas, according to Chinese meteorological forecasters.

The Central Meteorological Observatory announced a yellow warning on Tuesday morning for several provinces including parts of Shandong, Anhui, Jiangsu, Zhejiang, Hubei, Hunan, Jiangxi, Fujian, Guizhou and Guangdong, and the Guangxi region.

China has a four-tier, colour-coded weather-warning system, with red representing the most severe warning, followed by orange, yellow, and blue.

Visibility on the Qiongzhou Strait that separates Guangdong’s Leizhou Peninsula from the island province of Hainan was less than 200 metres, prompting the Hainan Meteorological Service to issue an orange alert and advise traffic, shipping, and other departments to take precautions, CCTV reported on Tuesday.

Three ports in southern Hainan’s capital Haikou showed intermittent suspension of navigation earlier on Tuesday morning, with two still suspending ships in and out of ports as of 10:00 am (0200 GMT), CCTV reported.

Multiple areas in China’s southeastern Fujian also issued alerts for heavy fog, with ferry crossings between Xiamen and Zhangzhou suspended, according to CCTV.

Fog will continue in the mornings and evenings of Qiongzhou Strait until Friday, and conditions for navigation will be poor, CCTV reported citing the national weather forecast bureau.

In December, one person was killed when more than 200 vehicles were involved in a pile-up on a bridge in China’s central Zhengzhou city due to heavy fog.