• Shares of India's Adani Group companies plunged after its billionaire chair Gautam Adani was indicted in a New York federal court.
• The 62-year-old billionaire and the other defendants are accused of paying over $250 million in bribes to Indian government officials to secure solar energy contracts that could generate more than $2 billion in profits.

India's Adani Group saw shares of its companies plunge Thursday after its billionaire chairman Gautam Adani was indicted in a New York federal court over his alleged involvement in an extensive bribery and fraud operation.

The 62-year-old billionaire and the seven other defendants have been accused of paying over $250 million in bribes to Indian government officials to secure solar energy contracts that could generate more than $2 billion in profits.

The Indian group's flagship firm Adani Enterprises fell 23%, while the company in the eye of the storm Adani Green Energy tanked 18.95%. Adani Energy fell 20%. 

Adani Power lost 14.48%, Adani Port's share price dropped 20%, while the group's retail arm Adani Wilmar shed 10%.

The benchmark NSE Nifty 50 Index slid 0.87%.

Adani, along with two executives from Adani Green Energy Limited — his nephew Sagar Adani and Vneet Jaain — have been charged with misleading U.S. and international investors about the company's adherence to antibribery and anticorruption standards while raising over $3 billion to finance energy projects.

Adani Green Energy has called off its plan to raise funds through U.S. dollar-denominated bonds, Reuters reported.

"These are very serious charges," said David Riedel, president and founder of Riedel Research Group. "They'll certainly be cut off from the U.S. markets," he said, adding that Adani may need to look for domestic funding sources.

Riedel also expects more pain in the Adani-affiliated stocks: "They're probably going to give back everything that they've gained in the last year or so."

The five-count indictment in U.S. District Court in Brooklyn also accused Ranjit Gupta and Rupesh Agarwal, former executives of the renewable energy firm Azure Power Global, along with three former employees of the Canadian institutional investor Caisse de Depot et Placement du Quebec — Saurabh Agarwal, Cyril Cabanes, and Deepak Malhotra.

CDPQ said it is aware of the charges filed. "Those employees were all terminated in 2023 and CDPQ is cooperating with U.S. authorities," the investor said in an email.

This comes after the conglomerate spent the bulk of last year attempting to move beyond the allegations of accounting fraud and "brazen stock manipulation" made by shortseller firm Hindenburg Research. 

"Since releasing our January 2023 report identifying Adani as the largest corporate con in history, we have never wavered in our view, nor has Adani ever refuted our findings," Hindenburg said in a statement to CNBC on Thursday.

The conglomerate had rebutted the claims, adding that it has "always been in compliance with all laws."

These charges do not change the "strong underlying fundamentals" of India's market or the country's growth trajectory, said Raymond James' head of advisory solutions and market strategy, Matt Orton. 

"Once the dust settles, there will be even better opportunities for long-term investors in India," he said.

—CNBC's Dan Mangan contributed to this report.