Indian billionaire Gautam Adani has been indicted by US prosecutors for his alleged role in a $US265 million ($A407 million) bribery scheme, plunging his conglomerate deep into crisis for the second time in two years.
The multiple counts of fraud levelled against Adani, who is one of the world's richest people, and seven other defendants, sent shares and bonds of Adani firms tumbling on Thursday.
Adani Green Energy, the company at the centre of the allegations, also cancelled a $US600 million bond sale.
Arrest warrants have been issued for Adani and his nephew Sagar Adani and prosecutors plan to hand those warrants to foreign law enforcement, court records show.
US federal prosecutors said the defendants agreed to pay the bribes to Indian government officials to obtain contracts expected to yield $US2 billion of profit over 20 years, and develop India's largest solar power plant project.
They also said the Adanis and another executive at Adani Green Energy's former CEO Vneet Jaain raised more than $US3 billion in loans and bonds by hiding their corruption from lenders and investors.
The three were charged with securities fraud, securities fraud conspiracy and wire fraud conspiracy.
Adani Green Energy cancelled plans for a $US600 million bond-raising following the indictments. (AP PHOTO)
The Adanis were also charged in a parallel US Securities and Exchange Commission (SEC) civil case.
"Gautam and Sagar Adani were engaged in the bribery scheme during a September 2021 note offering by Adani Green that raised $US750 million, including approximately $US175 million from US investors," the SEC said in a press statement.
"The SEC's complaint against Gautam and Sagar Adani charges them with violating the antifraud provisions of the federal securities laws," it said.
"The complaint seeks permanent injunctions, civil penalties, and officer and director bars."
The charges follow much turmoil for the Adani Group in 2023 after short-seller Hindenburg Research issued a report that accused it of using offshore tax havens improperly, which the company has denied.
Shares in Adani Green Energy plunged 17 per cent and stocks for many other firms in the conglomerate lost more than 10 per cent.
The group lost $US28 billion in value in Thursday trade, putting its firms' combined market capitalisation at $US141 billion.
Before the Hindenburg report in 2023, the group's market value was $US235 billion.
Adani dollar bonds slumped, with prices down 3-5c on bonds for Adani Ports and Special Economic Zone.
The unsealed criminal charges by the US Attorney's Office for the Eastern District of New York showed some conspirators referred privately to Gautam Adani with the codenames "Numero uno" and "the big man", while Sagar Adani allegedly used his cellphone to track specifics about the bribes.
Five other defendants were charged with conspiring to violate the Foreign Corrupt Practices Act, a US anti-bribery law, and four were charged with conspiring to obstruct justice.
None of the defendants is in custody, a spokesperson for US Attorney Breon Peace in Brooklyn said.
Gautam Adani is believed to be in India.
Gautam Adani is worth $US69.8 billion according to Forbes magazine, making him India's second-richest man after Mukesh Ambani.
He is one of the few billionaires formally accused in the United States of criminal wrongdoing.
Shares in GQG Partners, an Australia-listed investment firm that is a major Adani backer, slid 20 per cent, its largest one-day fall since it listed three years ago.
It said in a statement that it was monitoring the charges.