Rep. Steve Scalise was shot in Alexandria, Virginia, Wednesday morning, Rep. Mo Brooks told CNN.
Brooks said he was on deck at a practice for the congressional baseball team when the shooting occurred.
Scalise, the majority whip, appeared to have been shot in the hip and it appeared two Capitol Hill police agents were shot, he added.
Brooks said there were a number of congressmen and congressional staffers lying on the ground, and at least one of them was wounded. The Alabama Republican said he used his belt as a tourniquet to help one of the victims.
He said the shooter appeared to be a white male but added that "I saw him for a second or two." He said the shooter was behind the third base dugout.
"The gun was a semiautomatic," Brooks said. "It continued to fire at different people. You can imagine, all the people on the field scatter."
Alexandria police said earlier Wednesday they were responding to a "multiple shooting" in the city. The tweet also said the suspect is in custody.