NEW DELHI — The value of Gautam Adani’s business empire has crashed by more than $50 billion this week since Hindenburg Research, a US firm that makes money from short selling, published a blistering report accusing it of fraud.

India’s Adani Group has denounced Hindenburg’s allegations as “baseless” and “malicious,” and it is considering legal action. But the sharp sell-off in shares, which began Wednesday, accelerated Friday after US hedge fund billionaire Bill Ackman said he found the short seller’s report credible.

Hindenburg Research published an investigation on Adani’s conglomerate late on Tuesday, accusing it of “brazen stock manipulation and accounting fraud scheme over the course of decades.” It said it had taken a short position in Adani Group companies, meaning it would benefit from a drop in their value.

Shares of those companies — some of which had surged over 500% in the last few years — plunged when India’s stock market opened Wednesday. The rout resumed Friday when trading resumed following a market holiday on Thursday.

Shares of Adani Transmission, Adani Total Gas and Adani Green Energy — three of the group’s seven listed companies — were down 20% each on Friday, while shares of Adani Enterprises, the conglomerate’s flagship company, fell 18%. Friday’s losses wiped out almost $39 billion in market value.

According to the Bloomberg Billionaires Index, Adani is still Asia’s richest man with a personal fortune worth $113 billion, $30 billion more than fellow Indian entrepreneur Mukesh Ambani. Friday’s losses will reduce that gap.

Hindenburg said Thursday that it stood fully by its report and believed any legal action would be “meritless.”

“If Adani is serious, it should also file suit in the US where we operate. We have a long list of documents we would demand in a legal discovery process,” the short seller said in a post on Twitter.

Hindenburg isn’t the first research firm to express concern about the finances of Adani’s sprawling empire, which has borrowed $30 billion to become established in industries ranging from logistics to mining, and is aggressively growing in diverse sectors such as media, data centers, airports and cement.

Ackman weighed into the debate on Twitter Thursday, saying he found the Hindenburg investigation “highly credible and extremely well researched.”

“We are not invested long or short in any of the Adani companies ... nor have we done our own independent research,” Ackman added.

Hindenburg’s claims come at a sensitive time. Adani Enterprises is aiming to raise 200 billion rupees ($2.5 billion) by issuing new shares this month. The offer will close on Tuesday.

A college dropout and a self-made industrialist, Adani is the world’s fourth richest man, ahead of Bill Gates and Warren Buffet. He is also seen as a close ally of India’s prime minister, Narendra Modi.

The 60-year old tycoon founded the Adani group over 30 years ago. — CNN