A man left a gun in a box outside a Brooklyn firehouse late Sunday — and sparked a major police response when he claimed it might be a bomb, cops said. 

The unidentified man walked up to FDNY Engine 290 on Sheffield Avenue near Livonia Avenue in Brownsville around 6:50 p.m. and left the box on the ground outside, police said. 

“I think this is a bomb,” he announced to those outside before walking off, cops said. 

The NYPD’s Bomb Squad was called to the scene, authorities said. 

Police ultimately determined that a gun was inside.

The person who allegedly dropped off the box was still at large Monday morning.