The FBI says it is "too early" to determine whether the shooting at the baseball practice of the Congressional Republican team is terrorism or an attempted assassination.

Special Agent Tim Slater held a news conference near the scene with Virginia Governor Terry McAuliffe, Capitol Police Chief Matthew Verderosa, and local Alexandria city police but no details about the investigation were confirmed.

The FBI has officially taken the lead on the case per normal procedure since members of Congress were involved.

Mr Slater said it was also "too soon" to confirm the identity of the shooter or the weapon used.

Congressman Mo Brooks said he did not get a detailed look at the gunmen but he appeared to be a heavyset, white male, brandishing a rifle.

There were five people taken to the hospital but Mr Slater and Mr Verderosa did not confirm whether that count included the shooter.

The Capitol Police Chief did confirm his two officers - who were on a limited security detail for House Majority Whip Steve Scalise - are "in good condition" after being shot by the gunman,

Congressman Rand Paul, who was playing in right field, said he heard at least 50 to 60 shots fired and Mr Scalise was moving after he was shot, dragging himself into the outfield.

Mr Flake said the shooter "had a lot of ammo".

Mr Brooks said there were approximately 25 members of the GOP baseball team at the practice this morning.