Two black boxes, placed inside the now-demolished twin towers in Noida for research purposes, have been recovered while discussions continued Thursday over the ongoing repairs in ATS Village and Emerald Court societies, officials said.

While the complete post-demolition structural audit of the critical residential towers located within 50 metres of the twin towers is yet to be done, around one dozen window panes in Emerald Court and three dozen in ATS Village developed cracks and were being repaired, the officials said.

A nine-metre stretch of a boundary wall was damaged and it also came to light that some common areas and residential towers in the critical zone had developed "cosmetic cracks", they said.

"Two black boxes which were placed inside the twin towers at the time of the demolition for research purposes have been recovered. There are eight more black boxes that are yet to be recovered," Dr Debi Prasanna Kanungo, senior principal scientist at the Central Building Research Institute (CBRI), told PTI.

"Other instruments like seismographs, thermal imaging cameras, photos and videos taken using drones that were deployed in surrounding areas of the twin towers are already with CBRI and the information collected by them is being analysed. The findings will help us in future studies, the scientist said.

Black box is an electronic device generally placed inside aircraft to record sound. They are widely used for their indestructible nature and research purposes.

Meanwhile, officials of Edifice Engineering, the firm which was tasked with the safe demolition of the twin towers, on Thursday met with the residents of the two societies to address concerns over repair works.

Mayur Mehta, the project manager for Edifice Engineering, said, "Repair works for window panes have already started and will be completed in the next few days."

He said Edifice has also hired a Kerala-based geo-structural consultant for the pre- and post-blast structural analysis and it would take it roughly another 10 days to submit its report.

"The repair work for cracks, which appear to be superficial and cosmetic in nature, will begin after the consultant's analysis report is received," he added.

Separately, real estate group Supertech, the developer of the twin towers, is expected to complete the post-demolition structural audit of the seven residential towers -- four in ATS Village and three in Emerald Court -- soon, according to officials.

The Noida twin towers are the tallest illegal structures to have been demolished by implosion technique in India yet. Prior to that, four residential complexes of 18-20 storeys in Maradu municipal area of Kochi, Kerala were razed in a matter of few seconds by implosion in 2020.

Both demolitions had come in compliance with orders of the Supreme Court which found the structures built in violation of building norms.