Officials say a loud boom was heard -- and felt -- in and around Highland Park Tuesday evening but the cause of the noise remains a mystery.

More than an hour after the explosion was heard, firefighters were still unable to determine its cause.

Dozens of calls came in at 8:02 p.m. reporting a "loud sound described by some as an explosion" in the vicinity of North Avenue 52 and Monte Vista
Street, Brian Humphrey of the Los Angeles Fire Department said.

Those hearing the sound included members of a nearby fire station about a half-mile from where the sound seemed to emanate, Humphrey said.

20 firefighters have combed the area looking for anything out of the ordinary, but have come up empty.

Police theorized the sound could have been a backfire, and some people
even theorized a meteorite, Humphrey said.

"It was far louder than anything we have experienced," Humphrey said.