By 10 a.m., over 2.8 million shares had changed hands via a block deal at Rs 782 per share. Over 4.5 million shares had exchanged hands on the BSE.
BT was supposed to sell about 5 per cent of its stake (7.5 to 10 million shares) in the Indian IT service provider for about $100 million.
The price band for the transaction was fixed at Rs 735 - Rs 790, a discount of 5 to 12 per cent from Tech Mahindra's Wednesday closing price of Rs 834.90.
JPMorgan and Credit Suisse are advising BT on the share sale.
Tech Mahindra, which provides technology services to telecoms companies including BT and AT&T, is majority-owned by Mahindra & Mahindra, India's larger maker of sports utility vehicles and tractors. British telecom is UK's biggest fixed-line telecoms company.
(With inputs from Thomson Reuters)