Shares in the main listed unit of Indian billionaire Gautam Adani's conglomerate nosedived 25 percent on Tuesday, before rebounding slightly, as election results suggested a reduced majority for Prime Minister Narendra Modi's party.

Adani is considered a longtime close associate of Hindu-nationalist Modi, both from Gujarat state.

Opposition parties and other critics have accused Adani of benefitting from their relationship to unfairly win business and avoid proper oversight.

Adani Enterprises pared losses slightly to close down 19 percent lower at $35.33 (2,950 rupees) per share, down $6.44 from Tuesday's open.

Shares in other Adani Group companies also crashed, with broadcaster NDTV down 19 percent and the conglomerate's ports division closing 21 percent lower.

"When Modi is losing, the stock market says... Adani will go as well," top opposition leader Rahul Gandhi told a press conference. 

"This means there is a direct relationship, a relationship of corruption."

Adani businesses were the biggest negative movers in what was the Mumbai stock exchange's worst day since the onset of the coronavirus pandemic four years ago, with the Sensex benchmark closing 5.7 percent lower.

Exit polls had predicted a landslide victory for Modi's Bharatiya Janata Party (BJP) and its allies in this year's election.

With more than 95 percent of votes counted, election commission figures showed Modi on course to win a third term but with a greatly reduced majority.

Last year Adani Group saw more than $150 billion wiped from its market value after a bombshell report by US investment research firm Hindenburg Research accusing it of "brazen" corporate fraud. 

The family-run conglomerate's founder saw his personal fortune collapse by around $80 billion as a result, but both Adani and his business have since pared much of those losses as public scrutiny receded.

Adani Group has denied the allegations of fraud documented in the report, last year calling it a "deliberate attempt" to damage the image of his conglomerate for the benefit of short-sellers.