The air in New Delhi, the world's most polluted capital, got even worse after people ignored a ban to fill the air with Diwali fireworks

• New Delhi is considered the world's most-polluted capital city.
• The toxicity of its air rose to dangerous levels this week, partly fuelled by fireworks.

Air pollution levels in New Delhi, India's capital city, got even worse after people ignored a ban and held firework displays to mark the festival of Diwali.

New Delhi is considered the world's most-polluted capital city, and had an especially poor day Friday, the day after Diwali celebrations.

Authorities typically ban fireworks for the festival in India, but people often use them anyway, Reuters noted.

This video shows fireworks in Delhi, and smog in the city:

Experts found on Friday that the city's air had an average of 706 micrograms of PM2.5 - a small and health-damaging particle - per cubic metre of air, Reuters reported.

Some parts of Delhi were at 999 micrograms on Friday, the BBC reported.

The World Health Organization says that levels it's unsafe to have an annual average above of five micrograms.

It says that these particles "can penetrate the lung barrier and enter the blood system" and that "chronic exposure to particles contributes to the risk of developing cardiovascular and respiratory diseases, as well as of lung cancer."

Indian authorities warned the conditions in New Delhi were "severe" and could damage people's health, according to Reuters.

The levels will take until Sunday to improve, and even then air quality would be qualify as "very poor," the BBC reported.