CHIANG MAI, April 4 -- Northern Thailand is once again under a blanket of toxic haze, with Chiang Mai facing one of its worst air pollution episodes in recent months as fine particulate levels surged to "extremely dangerous" levels, according to The Nation.

PM2.5 concentrations at Nakornping Hospital in Mae Rim district hit 409 micrograms per cubic metre at about 9am today - a level far exceeding safe limits and considered hazardous to human health.

Images from the area showed thick smog engulfing the city, reducing visibility so severely that nearby buildings were barely discernible.

Health officials warned the crisis is already affecting patients, particularly those in vulnerable groups, with many reporting breathing difficulties as ...