The developer of the 398 unit Axis apartments on Dallas and Montrose estimates the damage to his complex is around $35 million.
Firefighters said it was one of the largest fires in Houston history and, as of now, investigators haven't ruled any cause out.
"There is welding, they are using cutting torches, so many things going on in a building under construction," said HFD Captain Ray Lozano. "There's so many variables, there's too much to tell."
Firefighters say the fast moving fire was fanned by high winds and perfect conditions for an inferno.
The building didn't have fire sprinklers or fire walls, items that usually slow a blaze.
"One of the most dangerous fires that firefighters can get involved with, is a building under construction," said Lozano.
The massive blaze also caused damage to nearby homes and businesses.
"I was really scared the fire was just going to jump," said Cathy Cordes, who lives across the street.
Flying embers burned her deck and the extreme heat cracked her windows. Other neighbors had smoke damage and melted shutters.
"We're alive, we're really grateful," said Cordes. "It could have been 100 times worse if it came across the street."
The complex's developer says he has been in touch with the homeowners association and expects his insurance company to work out the costs of repairs.