Officers arrived and learned that Ruben Rivera, 43, and 29-year-old Manuel De Jesus Aguilar were under water and had not come up.
The Liberty Fire Department along with Texas Parks and Wildlife, Tarkington Volunteer Fire Department and the Cleveland Volunteer Fire Department responded to the scene and began rescue operations.
Witnesses said Rivera and De Jesus Aguilar were trying to swim across the Trinity River, and they went under the water somewhere in the middle.
Officials searched for more than two hours Saturday night and resumed their search at sunrise Sunday.
The search teams are combing the river from about 100 yards north to 100 yards south of where the pair was last seen.
Search boats are also following the current further down the river in an effort to locate the two missing swimmers.