Not Delhi but Pakistan's Lahore has become the world's most polluted city with an Air Quality Index of 1,900 on Sunday, which is its highest ever, media reports said.

The worsening situation has prompted Pakistan to write a letter to the Indian government for a dialogue on the issue.

The Pakistani government imposed emergency measures like closing schools and issuing work-from-home mandates after its AQI was recorded at least six times more than the World Health Organisation (WHO)-defined limit.

Citizens have been urged to stay indoors, keep doors and windows shut.

People have been asked to avoid unnecessary travel while a ban has been imposed on three-wheeler rickshaws.

The government has also stopped all construction works in certain areas to reduce the pollution levels.

Pakistan's level of PM2.5 pollutants, which includes fine particulate matter in the air having the potential to cause deadly health impacts, peaked at 610, which is 40 times more that the limit of 15 in 24 hours, as per WHO guidelines.

Speaking to CNN, Secretary for Environment and Climate Change Raja Jahangir Anwar said: "We need climate diplomacy, as a regional and global issue."

"We are suffering in Lahore in a way due to the eastern wind corridor coming from India. We are not blaming anyone, it's a natural phenomenon," he said.

Like in northern India, pollution spikes in Pakistan during winters leading to health complications among residents.

Meanwhile, Delhi AQI stood at 276 on Monday afternoon.