Lahore, Nov 7 (IANS): Pakistan's Lahore city closed schools on Thursday after an alarming rise in air pollution that made it the world's most polluted city for a few hours, covered by a dark toxic cloud.

"Due to sudden increase in smog, all schools in Lahore will remain closed," Usman Buzdar, the head of the government of Punjab province, whose capital is Lahore, tweeted.

Buzdar said his administration was taking action against the burning of agricultural waste and other factors that caused smog and the spike in pollution, Efe news reported.

On Wednesday night, the concentration of PM 2.5 particles (less than 2.5 microns and considered the most harmful for health) was 580 per cubic meter in Lahore, making the city the most polluted in the world for a few hours, according to the Air Quality Index of the US Environmental Protection Agency.

By Thursday morning, rain and wind had dispersed the toxic cloud and the concentration of PM 2.5 particles came down to the 138, which is still harmful.

Punjab Environment Protection Department spokesperson Naseem ur Rehman blamed India for the burning of crop residue that the increased the pollution levels.

"The trans-border wind brought smoke that specially hit areas bordering India," he told Efe news.

Air pollution is so common in this city of 11 million inhabitants that the period between October and January is known as the "smog season", caused by vehicle emissions and the burning of stubble.