A gunman opened fire on Republican members of Congress during a baseball practice near Washington early on Wednesday, wounding several people including House of Representatives Majority Whip Steve Scalise before being taken into custody, police and witnesses said.

In a dramatic blow-by-blow account, Representative Mo Brooks of Alabama told CNN the gunman was armed with a rifle and appeared to be a white male, "a little bit on the chubby side."

Brooks said he saw the man only for a second, and that he was shooting from a chain link fence behind the third base position on the field where the congressional group was holding its morning practice.

"There must have been 50 to 100 shots fired," he told CNN. "I hear Steve Scalise over near second base scream. He was shot," said Brooks, adding he helped apply a tourniquet with his belt to a congressional staffer who was shot in the leg.

"One of our security detail was shooting back, but it was our pistol versus the shooter's rifle," Brooks said. "The only weapon I had was a baseball bat."

Fox News anchor Bret Baier tweeted that Scalise was shot in the hip and is expected to survive.

Scalise's position as whip in the Republican-controlled House makes him one of the most senior figures in Congress. He is a representative from Louisiana.

U.S. President Donald Trump, a Republican, said he and Vice President Mike Pence were aware of the shooting and are monitoring developments closely.

"We are deeply saddened by this tragedy. Our thoughts and prayers are with the members of Congress, their staffs, Capitol Police, first responders, and all others affected," Trump said in a statement.