The fire has burned more than 1,300 acres of public and private land near Black, Missouri, 115 miles southwest of St. Louis. The fire was discovered Sunday. The cause is under investigation.
Federal authorities say that about 40 percent of the fire has now been contained. Nearly 150 firefighters from as far away as Iowa and Minnesota are helping.
About 30 homes and other structures are at risk, but no buildings have been damaged no one has been hurt.
The biggest wildfire on record at the Mark Twain National Forest is believed to be a 2011 blaze that burned nearly 5,000 acres.