UPDATE: As of 3:45 p.m., the first had been knocked down after assistance from the National Airport Foam Unit. It was caused by an underground transformer in front of the building. The fire is a fairly spectacular one, with flames shooting out of grates and frequent violent explosions. Connecticut Avenue is closed between T and Calvert Streets in both directions, and parts of Florida and T Street had been cordoned off at various points this afternoon.

A DCist tipster sends us this image of smoke pouring out of an office building located at 1875 Connecticut Avenue NW. The building has been evacuated. D.C. Fire and EMS are on the scene and are currently working on containing the fire. According to our source, the blaze is causing explosions, so firefighters are exercising extreme caution. We’ll keep you updated if we get new information — so far, we haven’t received reports of any injuries.