The Harris County Sheriff's Office said Precinct 4 was called out at about 11 p.m. to a Champions-area apartment complex off FM 1960.
Deputies said when they got there, they discovered that a 4-year-old girl was by herself in a closet when she found a gun and shot herself. The girl was taken to the hospital, where she died, HCSO said.
The sheriff's office said the little girl's mom and 10-year-old sibling were home at the time.
Investigators said the gun belonged to the girl's mother.
"The firearm does belong to the mother. She owned the firearm, and she indicated it was inside the closet. That's where it was stored at," HCSO Sgt. Jason Brown said. "That's how the child ended up finding it."
He went on to say it does not seem like the gun was secured.
"We are in the process of interviewing the mother and the 10-year-old child who was home at the time, trying to determine exactly how the child got in the closet -- you know, how this happened, as far as how the child found the firearm. But as of right now, we believe it's going to be accidental," Brown said.
It's unclear at this point if the mother will be charged, but the sergeant said charges are possible.