(Reuters) - Billionaire investor Bill Ackman's Pershing Square Capital Management will buy 9 million newly issued shares of real estate developer Howard Hughes Holdings ( HHH ) for $900 million, the companies said on Monday.

The agreement will increase Pershing's stake in Howard Hughes to 46.9% from 37.6% it currently owns, the companies said.

Ackman plans to use the acquisition to create what he has called a "modern-day Berkshire Hathaway," turning the real estate firm into a holding company that acquires controlling stakes in smaller businesses.

Howard Hughes had previously rejected Ackman's $900 million bid for 10 million shares in March, which would have raised Pershing's stake in the company to 48%, calling the proposal "not acceptable in its current form."

(Reporting by Shivansh Tiwary in Bengaluru; Editing by Shinjini Ganguli)