The wildfire is happening northwest of FM 1725 and Alsobrooks Road in San Jacinto County, according to Montgomery County officials.
At 8:16 p.m., officials said the wildfire was 10% contained.
SkyEye flew over the scene, where two Type 3 helicopters were seen dropping water at the Sam Houston National Forest.
The Texas A&M Forest Service said firefighters are working to create a containment line, while helicopters drop water from above.
As of 9:46 p.m., officials say that at least 300 homes have been threatened by the wildfire.
A shelter opened in Coldspring around 8 p.m. on Wednesday, according to officials.
Montgomery County officials said that residents off of Pauline Road, Lee Turner Road, Kirby Road, Big Buck Road, Hereford Way, Blue Teal Road should evacuate immediately.