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)