At least 17 incidents of people getting injured with these threads ('manja') were reported on August 15 when the kite flying activities peak on Independence Day.
The National Green Tribunal (NGT) in 2016 had put a ban on Chinese-origin 'manja' which is coated with tiny pieces of glass that often cause fatal cuts.
The court only allowed the use of cotton threads or any natural fibre that is free from metallic or glass components. The Chinese 'manja' is made of nylon or synthetic thread treated with glass and metal to make it sharper.
Unlike the cotton thread, it does not break on impact but cuts through the skin. These strings are also heavy conductors of electricity.
Any violation of the ban attracts a jail term of up to five years and a fine of up to Rs 1 lakh or both.
Some Delhi Police officials claim that the 'manja' is still being sold in many areas such as Patel Nagar, Vikaspuri, Janakpuri, Mayapuri, Shadipur, Tilak Nagar, Narela, Alipur, Mundka, Bawana, Kanjhawala, Kiradi, Begampur, Prem Nagar, Mangolpuri and Sultanpuri.
These threads mostly come from Western Uttar Pradesh cities like Bareilly where they are not banned.
On August 15, 17 cases were reported in the national capital, including one where an engineer died, while the others received severe deep cuts.
The police said they raided at least 17 shops on Thursday and booked them for selling the banned item.
Not just humans, but People for the Ethical Treatment of Animals (PETA) received 1,000 calls of injuries to birds due to kite strings on Thursday. Their wings were cut. In many cases, wings got completed separated.
One of the officials included in the policy making at PETA, which was part of the committee formed by Delhi's Lieutenant Governor in 2016 to look at imposing a ban on 'manja' said: "Banning manja in one state is no solution. It has to be done across the country because manufacturing is done in Bareilly and other parts of Uttar Pradesh. There must be a tight vigil on Delhi borders through the year."
Even power discoms have reported outages due to kite thread. A BSES spokesperson said: "People should enjoy kite flying, but they should do it responsibly. We advise residents not to fly kites near electricity installations, including overhead cables, and certainly avoid using metal or metal-coated 'manja'."
( With inputs from IANS )