St. Louis, MO  (KTRS)  The cause of three structure fires overnight in north St. Louis is being investigated.

The first fire broke out around 3:30 a.m. Wednesday at a four-story warehouse on Helen at Mullanphy, near the site of the new NGA headquarters. When firefighters arrived, the building was fully engulfed.

While firefighters were battling that fires, two nearby structures also caught fire. The incident quickly went to four-alarms, bringing out about 100 firefighters.

One person was taken to the hospital for smoke inhalation.

One of the structures was reportedly the historic James L. Clemons House. James Clemons was a relative of Samuel Clemons, Mark Twain.