The tiled domes and vaults on the lower level of the commuter rail station were created by Spanish immigrant Rafael Guastavino, who arrived in New York in 1881. They carry sound across the arc of the ceiling, enabling visitors to whisper to each other from diagonal corners.

"After a century in place, the mortar has weakened and some tiles are loose," said George Monasterio, the chief architect for Metro-North, which operates and maintains the station.

Guastavino used layers of thin, glazed tiles in a distinctive herringbone pattern on the ceilings. All loose tiles will be replaced to match existing tiles in what Monasterio described as a "painstaking effort."

The renovation of the building, commonly referred to as Grand Central Station and one of the New York's most visited tourist attractions, is expected to be completed by November, before the busy Christmas season and the 100th anniversary of the station next year.

With 44 platforms and 67 tracks, it is the world's largest train station in terms of platform capacity, according to railway-technology.com, and the busiest train station in the United States.

It is not unusual for nearly a million people to pass through the station on a given day, according to the Metropolitan Transportation Authority.

With its Beaux-Arts architecture and magnificent main concourse with its oversized map of the constellations, it is also considered one of the country's most beautiful public buildings.

The station has been featured in several films, including Alfred Hitchcock's "North by Northwest," "The Cotton Club" and "The Fisher King," in which the main concourse was transformed into a ballroom.

(Reporting by Patricia Reaney; editing by Christine Kearney and Dan Grebler)

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