A fine dust warning and an ultrafine dust advisory in the capital city have been concurrently issued as of 5:00 a.m. Monday, according to the Seoul Research Institute of Public Health and Environment. 

This comes as the average fine dust concentration across Seoul's 25 districts rose to 366 and 427 micrograms per cubic meter at 4:00 a.m. and 5:00 a.m., respectively, with ultrafine dust hitting 92 and 99 micrograms per cubic meter at the same time.

The institute said the dust particle levels are assessed to have spiked after yellow dust from Mongolia and China, as well as external air pollutants, entered the country's atmosphere.

City officials highly recommended people with respiratory and cardiovascular diseases, seniors and children to refrain from outdoor activities and urged everyone to wear protective masks outside.