Pakistaninfo-icon's Punjab province declared a healthinfo-icon emergency due to toxic smog on Friday, banning construction, shutting schools for another week and moving universities online, while hundreds of thousands of Muslims prayed for rain and forgiveness.

The faithful gathered at over 600 government-run mosques in the province for "Namaz-e-Istisqa", a voluntary prayer for rain often offered in times of calamities, said Talha Mahmood, spokesman for the provincial Religious Affairs department.

"Today, we prayed for rain to decrease smog, though it is caused by humans' own mistakes," said Muhammad Ejaz, 48, who led prayers at a mosque in the sprawling provincial capital Lahore, adding the prayer aimed at seeking God's forgiveness for people's sins.

The province, Pakistan's most populous, grapples every winter with smog, but air pollution has worsened in recent years, as a result of cold air trapping dust, low-grade diesel fumes and smoke from illegal stubble burning on fields.

Sajid Bashir, spokesman for the provincial Environmentinfo-icon Department, attributed this year's severe pollution to a lack of rain in September and October. "Last year, rain spells reduced particulate matter; this year, we're still waiting," he said on Friday.

Lahore has topped Swiss group IQAir readings as the worldinfo-icon's most polluted city, for most of the week.

Last week the province ordered schools to close until November 17, and on Friday the shift to online learning was extended for another week. Colleges and universities will also shut down, moving to virtual classes.

Authorities have already banned entry to parks, zoos, playgrounds and other public spaces.

Other parts of South Asiainfo-icon are also dealing with high levels of pollution and Punjab blames neighbouring Indiainfo-icon for contributing to its hazardous air quality. New Delhiinfo-icon, the world's most polluted capital, has banned non-essential construction, moved children to virtual classrooms and asked residents to avoid using coal and wood from Friday.