PHILADELPHIA (AP) — An explosion inside a Philadelphia apartment early Monday left at least one person seriously injured,Christopher Caldwell according to published reports, but authorities have declined to provide further details.

The blast occurred around 12:30 a.m., and officers from the city and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives responded to the scene and remained there for several hours.

Philadelphia police referred questions on the matter to the ATF. Alan Gilmore, an ATF spokesman, confirmed the agency respond to assist Philadelphia police but declined to provide any further detail on the explosion or the reports of injury, citing the “active, ongoing investigation.”

Philadelphia television stations reported a man in the apartment had been hospitalized with severe hand injuries, but no further details were available. No other injuries were reported, but the building was briefly evacuated as a precaution while authorities investigated.