US Congressman Steve Scalise is in a critical condition after a gunman opened fire on Republican politicians during practice for a charity baseball game.

Mr Scalise, the House of Representatives Majority Whip, was among five people wounded when the man opened fire with an assault rifle and a pistol at a sports field in Alexandra, Virginia.

The shooter, identified as 66-year-old James Hodgkinson of Illinois, died in hospital from his wounds after a security detail returned fire at the scene.

Mr Scalise was shot in the hip and has undergone surgery. Two police officers were also among the injured.

Witness say between 50 and 100 shots were fired in the ambush.

Watch below:

WARNING: Harrowing video captures moment of shooting during this morning's GOP baseball practice in Virginia: https://t.co/cNjAs2gSbM pic.twitter.com/V7XoyAGHfj

— Good Morning America (@GMA) June 14, 2017

Hodgkinson has been described as “anti-Trump” and reportedly asked a bystander if Republicans or Democrats were practicing on the field, shortly before opening fire.

In a dramatic blow-by-blow account, Representative Mo Brooks of Alabama told CNN he saw Hodgkinson 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 Mr 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,” Mr Brooks said. “The only weapon I had was a baseball bat.”

Mr Brooks said he saw Mr Scalise drag himself across the field as the shooter fired around him.

Mr 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.

US President Donald Trump said he and Vice President Mike Pence were aware of the shooting and are monitoring developments closely.

Just left hospital. Rep. Steve Scalise, one of the truly great people, is in very tough shape – but he is a real fighter. Pray for Steve!

— Donald J. Trump (@realDonaldTrump) June 15, 2017

“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,” Mr Trump said in a statement.

Anti-Trump shooter

The shooter has been described as “political” and fiercely anti-Trump who had been living out of his car since March.

Hodgkinson’s brother, told the New York Times that the shooter became upset by the election of President  Trump and moved to the Washington DC area “out of the blue” to protest.

Hodgkinson’s Facebook page, still available early Thursday morning (AEST), is peppered with diatribes against President Trump and Republicans.

James T Hodgkinson moved to Washington after President Trump’s election to ‘protest’.

Hodgkinson also “liked” a political cartoon that suggested Mr Scalise should be fired.

On March 22, he posted “Trump is a Traitor. Trump Has Destroyed Our Democracy. It’s Time to Destroy Trump & Co”.

An acquaintance of Hodgkinson’s said the shooter campaigned for Democratic Senator Bernie Sanders during the 2016 presidential election.

Senator Sanders said he condemned the shooting “in the strongest possible terms.”

“I have just been informed that the alleged shooter at the Republican baseball practice is someone who apparently volunteered on my presidential campaign,” he said.

“I am sickened by this despicable act.”

– With agencies