Delhi’s pollution has once again soared to hazardous levels, with a top expert warning that India’s toxic air will have a bigger impact on public health than the Covid-19 pandemic.

On Wednesday, the air quality was 35 times over the safe limit set by the World Health Organization (WHO), leaving residents complaining of breathing problems, as well as itching in their eyes and throat.

Authorities have urged people, especially children and the elderly, to stay indoors as much as possible, while doctors recommend wearing a mask.

But Frank Hammes, global chief executive of air technology company IQAir, warns this is just a short term measure – and much more needs to be done.

“Alarming air pollution levels are a public health pandemic,” he told the BBC, explaining how toxic air impacts everything from mortality to IQ levels.

“This is going to have a much bigger impact on public health than Covid-19.”

Every winter, Delhi and nearby states face high pollution due to low wind speeds, vehicle emissions and the burning of crop remains and firewood.

According to IQAir, a Swiss air quality index, pollution in parts of Delhi surpassed the 550 mark on Wednesday morning, far exceeding even the “hazardous” level of 300.

London, in comparison, had a level of 26 early on Wednesday.

The Air Quality Index (AQI) measures the level of tiny particles in the air, also known as PM 2.5 – which Mr Hammes explains is “the most dangerous pollutant” and the “only determinant” for calculating pollution levels.

“It causes breathing difficulties, asthma attacks, heart and lung issues that send people rushing to emergencies,