The Houston Police Department responded to the Gateway on Cullen Apartments around 9:30 p.m. after reports of a shooting.
Lt. Riley said the gunfire erupted as two unidentified people began shooting at each other, causing partygoers to run in different directions.
Officials did not elaborate on what may have led the two gunmen to open fire at each other.
One woman reportedly fell and was trampled, and a man was struck in the head by the gunfire.
The man was taken to the hospital, where his condition is critcial. The woman was treated on the scene and released.
Houston police urge anyone with information on this shooting to call Crime Stoppers at 713-222 TIPS( 8477) or anonymously submit an online tip.