The cost of the World Trade Center ballooned by nearly $4 billion over the last four years � a wild spending spree that went completely unchecked by the Port Authority, according to a new audit.

The agency couldn�t even show documentation for the huge increase in costs, said the independent audit, which was released yesterday.

PA brass were �unable to produce supporting detail and source documents for the growth in cost estimates,� the audit stated.

The unprecedented 35 percent surge sends the total gross costs to $14.8 billion, a $3.8 billion jump from the 2008 forecast.

When the construction is complete, it�s likely the PA will have spent a whopping $7.7 billion of its own money on the effort � a $1.7 billion hike.

The higher costs were the results of several factors � from the rush to finish the 9/11 Memorial in time for the 10-year anniversary to higher insurance costs, according to auditors.

The review is the first in a two-part, top-to-bottom accounting of the agency, ordered by Govs. Cuomo and Chris Christie when they approved massive toll hikes.

(Source: NY Post)