Toxic smog in eastern Pakistan has made thousands of people sick, forcing authorities to shut some cities for the rest of the week.

Smog in the country's second-largest city Lahore has risen to dangerous levels.

The Punjab provincial government has ordered that schools, offices, malls and parks in three cities, including Lahore, be closed until Sunday.

Pakistan's Punjab province borders the Indian state of the same name.

Over the past few days, Lahore's Air Quality Index - which measures the level of fine particulate matter in the air - have hovered around the 400 mark. AQI levels at or below 100 are generally thought of as satisfactory. Lahore borders the Indian city of Amritsar.

North India is also suffering from the impact of toxic smog.

Air pollution in the Indian capital Delhi has risen to alarming levels. On Tuesday, the air quality index for the Indian capital hit 300 on 7 November, nearly reaching the hazardous levels of 301-500.

Some Lahore residents told BBC Urdu that the noxious atmosphere is a frequent affair that has severely affected their health and other daily activities.

"It feels like this poisonous atmosphere has become a part of our lives," said salesman Ameer Hamza, whose work requires him to be out and about on a motorcycle for much of the day.

"I go to various points to market products and when I go home after a long day, my eyes are red and irritated due to air pollution. And then my work is affected due to me being sick very often. Right now, I am nursing a cold, sore throat, and cough," he said.

Sarah Zeeshan said her one-and-half-year-old daughter has found it difficult to eat and drink as the smog has led to blisters forming all around her mouth.

Persistent exposure to smog can lead to longer-term health damage, including causing lung cancer.

Some experts believe the burning of crop residue to prepare for the winter planting season is a key cause of the air pollution.

Pakistan said last week that it will raise the issue with Indian authorities at a diplomatic level, local media reported, without giving further details.

But experts have noted that just as in India, farmers in Pakistan also resort to stubble burning to prepare for a new planting season.

Medical facilities, grocery stores and gas stations remain open in Punjab. Authorities have advised residents to wear masks if they must go outside.

Environmentalist Rafi Alam said the government policies aimed at combating smog are "made only in haste, which are of no use".

"Until you recognise a problem as a problem, how can you fix it? Will sprinkling water or closing schools three days a week solve the smog problem?" he said.

According to the Air Quality Life Index produced by the University of Chicago, air pollution shortens people's lives by almost seven years in Pakistan's most polluted regions, including Lahore.