FALLS CHURCH, Va. — An underground transformer exploded, and about 250 mostly elderly residents evacuated their apartments in suburban Washington, D.C.

Lt. Willie Bailey of the Fairfax County Fire Department said it was unclear what caused the transformer to explode at about 8 a.m. today in the Seven Corners area.

Residents of a nearby apartment complex for the elderly and disabled were being taken to a school as a precaution while investigators looked into what happened.

No injuries were reported.

Bailey said about 60 firefighters responded and put out the fire.