Tragedy was averted this morning when a homemade bomb inside a vacant Jersey City pizzeria was disarmed by authorities.

The bomb — a 2.5-gallon gasoline can with a wire running from it to a light fixture and another wire attached to the front door — had been placed in the front of the building and was rigged to go off when someone opened the front door at 451 Palisade Avenue.

“It was just dumb luck,” that firefighters entered the building through the back door instead of the front, said one firefighter at the scene who is isn’t authorized to speak to the media.

The pizzeria on the first floor was recently vacated, neighbors say, and there are apartments above it. The first floor was filled with natural gas, as the gas line had been cut, apparently with the intent of increasing the damage and loss of life tenfold.

The drama started at about 6:40 this morning when the Fire Department received a call from tenants there who said they were being overcome by natural gas fumes. At about the same time, the owner of the building called police to report a burglary, Jersey City Deputy Police Chief Peter Nalbach said.