BENGALURU, June 4 (Reuters) - Indian shares plunged 6% in their worst intraday percentage fall since the onset of the COVID-19 pandemic on Tuesday, as early vote-counting trends showed Prime Minister Narendra Modi's alliance falling short of a predicted landslide victory.

The NSE Nifty 50 index was down 6.2% at 21,824 points as of 12:02 p.m. IST, and the S&P BSE Sensex fell 6.1% to 71,900.

The indexes saw their worst fall since March 2020, and erased all of Monday's gains after exit polls projected that the BJP-led alliance will likely get a two-thirds majority in the lower house.

TV channels showed the ruling National Democratic Alliance was ahead in nearly 300 seats. 272 seats is the minimum needed for a simple majority in the 543-member lower house of parliament.

The volatility index jumped to its highest since March 2022 at 29.79, after easing on Monday.

"Since exit polls were at an extreme, anything that doesn't point to more strength is obviously a negative," said Anand James, chief market strategist at Geojit Financial.

"Despite exit polls giving a resounding victory for the ruling party, markets volatility gauge did not go down below 20, as it was pricing in an outlier," James added.

All sectors were in the red. Bank stocks fell 7.8%, realty dropped 9.1%, infrastructure declined 10.5%, while oil and gas stocks lost 11.7% and state-run companies and banks retreated 17% and 16%, respectively.

Adani Enterprises and Adani Ports were top losers in Nifty 50 index, falling 19%, each. Other Adani group stocks were down between 9-19%. The group stocks had jumped between 4%-18% on Monday after the exit polls.

"The fear of the market is whether present numbers will stay or will reduce further. (Even at current majority) there will be some element of disappointment as they are below market expectations," said Mayuresh Joshi, head- equity research India at William O’Neil and Company.

"Markets were at an all-time high, a lot of hope was built up (on BJP's majority) and these will unwind over the next few sessions and the focus will turn to policy announcements as the reforms will any way continue with BJP getting an absolute mandate," Joshi said. (Reporting by Sethuraman NR in Bengaluru; Editing by Varun H K)