NEW DELHI (Reuters) - Toxic smog has shrouded Pakistan's eastern city of Lahore for days as surging pollution spurs authorities to curb activities and set up a panel to oversee preventive efforts.
Here is a look at what causes the hazardous air, and how the government is tackling it.
WHERE IS LAHORE?
The capital of Pakistan's most populated province of Punjab, Lahore is just 25 km (16 miles) from the border with India, and is considered the cultural capital of the country.
Pakistan's second-largest city after the southern port city of Karachi has a population of about 13 million, and is a key hub for commerce, banking, and industry.
HOW BAD IS LAHORE'S AIR QUALITY?
Swiss group IQAir, which draws data from 14 regional monitoring stations, rated Lahore the world's most polluted city on Wednesday, with an air quality index (AQI) score of 1165, more than 120 times the levels recommended by the World Health Organization (WHO).
Pollution rose to unprecedented levels on Sunday on the city's outskirts, with a score of 1900.
WHAT CAUSES THE TOXIC AIR?
Several parts of South Asia suffer pollution every winter as cold air traps pollutants, such as emissions, dust and smoke from burning on farms to clear the remnants of rice crops before wheat is planted.
Lahore officials have previously blamed pollution on vehicle fuel of poor quality, as well as construction and industrial activity.
This year, however, more than ever before, the provincial government has blamed toxic air wafting in from neighbouring India, where northern regions are also battling hazardous air.
The Indian capital of New Delhi was the world's second most polluted city on Wednesday, with a score of 299, IQAir said.
WHAT SORT OF CURBS HAVE BEEN IMPOSED?
The government has closed primary schools, banned three-wheelers or rickshaws, halted some building work, and told people to stay indoors. It has also set up a "smog war room" to monitor the situation and oversee action to combat the pollution.
HOW WILL THE ISSUE BE RESOLVED IN THE LONG RUN?
Punjab plans to approach India through the foreign ministry for talks to thrash out a solution to the toxic air.
"We are hopeful that India will respond positively," Punjab senior minister Marriyum Aurangzeb told the Indian Express newspaper in an interview published on Wednesday.