The victims were among those who made 911 calls to report the fire, Hoover Fire Department spokesman Rusty Lowe said. Firefighters knew the women were trapped in their second-floor room, but couldn't get to them because of the flames.
"Half of the hotel was on fire. The fire was very hot and it was just difficult to reach all the rooms to get to the victims," Lowe said.
Two of the victims were 18-year-old cousins. They were identified by officials and a relative as Alondan Turner and Catherine Muse, both of Cordova, Ala., which is about 30 miles north of Hoover.
The local fire department has requested help with the probe from state and federal agencies.
"The investigation will reveal a lot more," Low said, adding that determining the cause "will not be a quick process, due to the amount of precision which will be required."
The Mississippi University for Women was established in 1884 as the first public college for women in the U.S., according to the school's Web site.