New York City has experienced an office building boom in recent years, and the prices of those properties have surged, too — but many investors view those prices beyond their real value and potentially heading for a fall.

The price New York City office REITs shares are, on average, 23% lower than private-market value of the buildings in their portfolios, the Wall Street Journal reports, citing data from BMO Capital Markets. The gulf between the two could suggest investors consider New York office assets overvalued.

While REIT share prices have traded below the private values of buildings for the past few years, real estate stocks have actually increased across the board in 2019. However, that is not the case for New York City REITs.

SL Green's stock price was 29.2% lower than estimated value last week, per WSJ, and Vornado's shares were at a 24% discount. SL Green CEO Marc Holliday acknowledged that NYC real estate was not a preferred asset class for stock market investors.

“If you look at these discounts, it’s trading like a broken asset class,” BMO Managing Director and stock analyst John Kim told the Journal.

Kim pointed to the city's office building boom, which means office landlords now have to compete fiercely for tenants. The past few years have seen vast amounts of new construction added to the city’s office supply, with millions more square feet coming online over the next year.

Hudson Yards, for example, has reshaped the office leasing landscape, luring major tenants to Manhattan's Far West Side and forcing the landlords of older buildings to upgrade in order to keep up with the new construction that is now on offer.

For now, the demand seems to be on pace with supply. Just over 9M SF of office space was leased in the first quarter of this year in Manhattan, a 20% jump on the year before, according to Colliers International. Availability rate increased to hit almost 10%, but asking rents reached an average of nearly $77 per SF, a new record.

The strong quarter followed a near-record office leasing year for the borough in 2018. Just under 42M SF was leased in Manhattan during the year — the highest yearly lease volume since 2001.