The 1.5 acre farm house in the uber rich neighbourhood at a stone's throw distance from Arabian sea was purchased by Mr Modi in 2004 for Rs 32 crore for hosting special parties for his clientele to show case his precious jewellery collection, they said.
The area has imposing farmhouses of the creme de la creme of cinema and the business world.
The "haut diamantaire's" expansive farm house, located about 100 km by road from Mumbai in Raigad district also has a 12,000 sq ft bungalow with five bedrooms, a large swimming pool, a movie theatre and a library, they said.
The agency had detected the property by analysing the documents recovered by it and had started searches yesterday. The CBI today sealed it till further notice.
Meanwhile, the CBI said it has no information about reports of Mr Modi having two passports "illegally".
The agency presented six persons arrested yesterday before special a CBI court in Mumbai which remanded them in custody till March 3.
The CBI had arrested Vipul Ambani, president (finance) of Fire Star Diamond, executive assistant Kavita Mankikar and senior executive Arjun Patil (all of Modi's companies).
Kapil Khandelwal, CFO of Nakshatra group and Gitanjali group, and Niten Shahi, manager of Gitanjali group were also arrested by the agency.
From Punjab National Bank, the CBI took into custody Rajesh Jindal, General Manager credit, at present posted at the bank's head office here.
Mr Jindal, who was the head of the Brady House, Mumbai, branch of the bank during 2009-11, was taken into custody last night, they said.
It is alleged that the issuance of Letters of Undertaking (LoUs) to Nirav Modi group firms without sanctioned limits started during his tenure.
It is alleged that Rs 11, 400 crore of LoUs were fraudulently issued to the firms of Nirav Modi and his uncle Mehul Choksi.