New Delhi, Oct. 1 -- Shares of automobile companies came under heavy selling pressure on Thursday, with the Nifty Auto index plunging more than 3% intraday to emerge as the biggest loser among sectoral indices. Weak September sales numbers from key automakers weighed on sentiment, while the government's new fuel-efficiency norms for passenger vehicles added another major development for the sector.

Bajaj Auto was the biggest decliner among the major auto stocks, falling 8%. Hero MotoCorp, Mahindra & Mahindra (M&M) and Eicher Motors declined around 4% each. Bosch, Ashok Leyland, Tata Motors Commercial Vehicles and TVS Motor Company also fell around 3% each.

Among auto ancillaries, Uno Minda, Samvardhana Motherson International and Bharat...