WASHINGTON: An elderly white supremacist with a history of anti-Semitic tirades has opened fire inside the national Holocaust Memorial Museum, fatally wounding a security guard before being shot by return fire.

Panicked tourists scattered, ducked and took cover as the shots rang out in the museum entrance shortly after noon in the heart of the US capital, not far from the White House.

The gunman was identified as 88-year-old James von Brunn, a Maryland resident who has served time in prison for taking a gun into the Federal Reserve, in an apparently botched anti-Semitic attack, a federal law enforcement official told AFP.

"It appears to be a lone gunman who entered into the museum and opened fire with what appears to be a rifle at this point," Police Chief Cathy Lanier said.

Police said the security guard, named as Stephen Tyrone Johns of nearby Maryland, was pronounced dead after being rushed to a nearby hospital.

The gunman was in critical condition, Mayor Adrian Fenty said.

President Barack Obama expressed his shock and sadness after the attack, saying the killing underscored the need to counter prejudice.

"I am shocked and saddened by today's shooting at the US Holocaust Memorial Museum. This outrageous act reminds us that we must remain vigilant against anti-Semitism and prejudice in all its forms," Obama said in a statement.

Von Brunn has written books on the Holocaust, Adolf Hitler, and his views on white superiority including "Tob Shebbe Goyim Harog," or "Kill the Best Gentiles," which his website calls "the culmination of his life's work."

In a recent posting on his blog, he railed that "America is a Third-World racial garbage-dump -- stupid, ignorant, dead-broke, and terminal."

Police and the FBI said they had no warning of the attack, which erupted at 12:50 pm just inside the packed museum, which is often visited by school groups, when the man walked into the entry foyer with what appeared to be a rifle.

"An armed gunman came into the entrance and immediately opened fire striking one security guard. There was fire, gunfire returned. The gunman was hit," said Mayor Adrian Fenty.

Former defense secretary William Cohen said he was standing outside with a museum official when the gunman entered, apparently from a red vehicle left parked in the street.

"When the shots rang out, we just ducked down and scattered," he said. "So we ran up the stairs. We didn't know how many shooters were there, how many shots were going to continue, how many people were involved."

"People panicked and wanted to evacuate the building. I said 'don't go down,'" said Cohen, who was at the museum because a play written by his wife Janet Langhart Cohen was to be staged there Wednesday evening.

Angela Andelson, 22, visiting from San Francisco, was walking toward the exit of the museum when she heard a loud bang "like someone had dropped something."

Then she saw a "gunman coming in (carrying) a long looking kind of gun.

"I just ran in to one of the exhibits to try to take cover," she said.

"People were screaming and ducking down, getting on the floor, getting under benches."

Another witness, Maria Hernandez, was with her grandparents walking through the haunting exhibits which chronicle the Holocaust and the genocide of six million Jews under the Nazis.

"We were in the exhibit 'Remember the Children' and we heard rounds fired and through the glass doors I saw a security guard firing towards the shooter and a man on his belly on the floor and when I looked back again, we were heading toward the exit, I saw blood all over the floor," she told AFP.

"He was hit real bad."

The FBI said it had sent members of a special response squad for the capital to support the police, but it had no information "to indicate threats to area landmarks."

The Israeli embassy issued a statement saying: "We are shocked and saddened by today's shooting incident."

More than 30 million people have visited the museum since its opening in 1993, including 85 heads of state.

Obama last week became the first US president to visit the Nazi death camp in Buchenwald, Germany where he renewed a historic commitment to Israel.

Flanked by Nobel laureate and Holocaust survivor Elie Wiesel and German Chancellor Angela Merkel, Obama laid a white rose at a memorial plaque for the camp's more than 56,000 victims.

He said Buchenwald was "the ultimate rebuke" to those "who insist that the Holocaust never happened, a denial of fact and truth that is baseless and ignorant and hateful."