ABU DHABI - Abu Dhabi Investment Authority (ADIA) said on Wednesday it had bought a 25% stake in 330 Madison Avenue from Vornado Realty Trust, gaining full ownership of the office block close to New York's Grand Central Station.

ADIA, which the Sovereign Wealth Fund Institute estimates manages nearly $700 billion in assets, has between 5% to 10% of its portfolio in real estate.

The stake was bought by a subsidiary of ADIA, a spokesman of ADIA told Reuters, adding ADIA already owned 75% of the property for 30 years.

ADIA did not disclose the value of the deal, but Vornado said on Monday it had agreed to sell its interest in the property as part of a "buy/sell process initiated by its 75% partner at a $900 million valuation."

The deal is expected to close in the third quarter of this year.

Gulf sovereign wealth funds, especially Abu Dhabi and Qatari funds, have for decades been investing in commercial real estate in Europe and the United States.

Vornado recently sold a non-controlling stake in its portfolio of New York properties along Fifth Avenue and Broadway in Times Square to Qatar Investment Authority (QIA) and private realty firm Crown Acquisitions in a transaction that provided the firm cash proceeds of about $1.2 billion.

Headquartered in the oil-rich capital of the United Arab Emirates, ADIA manages a global investment portfolio across more than two dozen asset classes.

(Reporting by Stanley Carvalho; Editing by Editing by Saeed Azhar; Editing by Mark Potter) ((stanley.carvalho@thomsonreuters.com; + 9712 6444431; Reuters Messaging: stanley.carvalho.thomsonreuters.com@reuters.net))