Indian conglomerate Adani Group said Wednesday that its airport unit would raise about $1 billion selling a minority stake to a group of investors including Singapore's Temasek and US firm BlackRock.

The transaction will see investors buy a 5.54 percent stake in Adani Airport Holdings (AAHL), one of India's largest private airport operators, giving it a "pre-money equity valuation" around $18 billion, a statement said.

The deal "represents one of the largest primary equity investments from financial institutions in India's airport infrastructure sector", it added.

Investors will subscribe to new equity shares of Adani Airport in three tranches, with the final leg expected to be completed by July 2027.

The money raised will be used to expand and modernise airport infrastructure, while scaling other businesses like ground-handling.

"We will continue to build capabilities within AAHL to scale it into the world's largest airports platform," Arun Bansal, chief executive of Adani Airport, said in a statement.

"This ambition is buoyed by the exponential growth opportunities across India, the rising spending power of the Indian consumer, and the momentum of our cityside developments as powerful economic catalysts in the country's major urban centres."

The fundraise comes as India's aviation sector is in the spotlight, with top two carriers Air India and IndiGo having faced several regulatory and safety challenges.

Indian airlines are expected to carry an additional 425 million passengers by 2044 -- more than double last year's figure -- but experts fear the growth has strained the system's ability to cater to the boom.

The investment also comes a month after billionaire-founder Gautam Adani resolved US bribery allegations -- a sign that his conglomerate is winning back the faith of global investors after years of regulatory overhang.