The $30 million price tag for a six-story, landmarked townhouse in Midtown that was purchased on Friday by developer Soho China from a Venezuela-owned bank got a boost from the Midtown East rezoning.

While the sale of the 13,349-square-foot mansion at 11. E. 51st St. equates to $2,247 per foot, there are also 19,783 square feet of air rights. Under the Midtown East rezoning scheme passed unanimously by the city council last Wednesday, the air rights are now worth roughly $6 million — and the City would score about $1.2 million towards public improvements.

About 6.5 million square feet of office space is expected to be built within the 70-block zone targeted for redevelopment. Currently, over 300 buildings are more than 50 years old and suffering from low ceilings, small windows and difficulty in adapting to modern technologies. These can now be replaced or built higher, and compete with the new skyscrapers on Manhattan’s far west side.

The possibility of shaving $5 million from the total price with the sale of the air rights added enough pop to the deal to create a bidding war among the suitors, said Victor Sozio of Ariel Property Advisors.

Ariel’s Sozio, Shimon Shkury, Howard Raber, Esq. and Jesse Greshin marketed the six-story building on behalf of Mercantil Commercebank, the US arm of a Venezuelan bank that bought it for $6.8 million in 1992 and transferred it between entities for $20 million in 2009.

The six-story building sits across from St. Patrick’s Cathedral and the Venezuelan consulate is next door.

Carrie Chiang of the Corcoran Group represented the buyer, China Soho, which is one of the largest office real estate developers in China and owns a stake in the GM Building.

The six-story ornate Italian Renaissance-style townhouse is just steps off Fifth Avenue, and is expected to be used for its offices. The beautiful interior has a projecting balcony and many intricate details. Only the exterior is landmarked.

Mercantil will remain under a sale-leaseback arrangement until it can move to new offices just two blocks away. A spokesman told The Post it will focus on commercial real estate instead of retail banking.

In 2011, Soho China paid $1.4 billion for the 40-percent stake in the GM Building at 767 Fifth Ave. along with the family of Moshe Safra. That same year, CEO Zhang Xin and her husband, Pan Shiyi, who jointly run China Soho, also bought a residential townhouse on East 74th Street for $26 million, beating out Brad Pitt.

More recently, the company is among others who have filed defamation lawsuits in New York against another Chinese billionaire, Guo Wengui, also known as Miles Kwok. Wengui is wanted by China for threatening to disclose Chinese corruption and is being sued there by some officials.

HNA Group, which owns a 25 percent stake in Hilton and bought 245 Park Ave., also filed a defamation lawsuit in New York against Wengui.

The townhouse on East 51 St. was designed by architect John H. Duncan, the designer of Grant’s Tomb, and was built between 1904 and 1906 as the home of Abby and John Pierce.

The stone contractor was known as the “Granite King,” as his firm was involved in the early subway system, as well as creating paving blocks and iconic buildings including the Customs House and the New York Public Library.