US President Barack Obama on Saturday opened a new museum in Washington that tells the history of African American life in the United States, starting with slavery and culminating with his 2008 election as the country's first black president.

"Today, as so many generations have before, we gather on our National Mall, to tell an essential part of our American story, one that has at times been overlooked," Obama said at the opening of the National Museum of African American History and Culture.

He noted that while history rightfully tells the stories "of the giants who built this country, who led armies into battle," it too often "ignored, or forgot, the stories of millions upon millions of others, who built this nation just as surely."

The new museum "helps to tell a richer and fuller story of who we are. It helps us better understand the lives, yes of the president, but also the slave, the industrialist but also the porter," Obama said.

With the backdrop of recent racial tension in the nation in the air, the president said the story the museum tells "perhaps needs to be told now more than ever."

The museum, Obama said, "provides context for the debate of our times, it illuminates them, and gives us some sense of how they evolved, and perhaps keeps them in proportion.

"Perhaps they can help a white visitor understand the pain and anger of demonstrators in places like Ferguson and Charlotte," he said, referring to the US cities where protests erupted after black men were killed by police.

The museum "reaffirms that all of us are American, that African American history is not somehow separate from our larger American story, it's not the underside of the American story ... it is central to the American story," he said.

Obama was joined at the ceremony by former president George W Bush, who signed the legislation authorizing the museum in 2003.

"A great nation does not hide its history," Bush said. "It faces its flaws and corrects them."

The museum depicts the impact of African American life on the country captured in artefacts, photographs and programmes.

The museum, which cost upward of 500 million dollars, opens a century after it was first proposed by African American Civil War veterans.

Director Lonnie Bunch said a "today a dream that was too long deferred is a dream no longer."

Also participating in the ceremony were a number of high-profile actors and musicians, including Oprah Winfrey, Will Smith, Robert DeNiro and Angela Bassett. Stevie Wonder performed, as did singer Patti LaBelle, who snuck in a pro-Hillary Clinton remark at the end of her song.

The museum joins other Smithsonian Institution museums on the National Mall, an open space in downtown Washington more than two kilometres long from the US Capitol to the Lincoln Memorial, with the needle-like Washington Monument in the centre.

The museum stands in the shadow of that obelisk to the nation's first president, who owned slaves at his Virginia farm but agreed they should be freed upon his death.

The museum's collection includes a violin given to a slave for the purpose of entertaining his owner, an intact slave cabin from South Carolina and an entire segregated train car.

There is the dress of Rosa Parks, who became a civil rights icon when she refused to give up her bus seat to a white passenger in 1955. The pen used a decade later by president Lyndon Johnson to sign the Voting Rights Act is included in the collection.

It also holds the Cadillac belonging to Chuck Berry, one of the forefathers of Rock and Roll, as well as Muhammad Ali's boxing gear.

The majority of the artefacts were donated to the museum, which Bunch said attempts to "help all Americans realize how much they've been shaped, informed and made better by the African American experience."

Kevin L Brown traveled from Los Angeles, California, to be among the thousands of people gathered on the mall for the ceremony.

"This isn't just for African Americans, this is for everybody," said Brown, himself African American.

Brown had an uncle who served in World War II and married a German woman. The uncle has since passed away, but his German wife will soon donate the congressional medal he won for his military service to the museum.

"It's funny how history is intertwined, not just in America, but all over the world," Brown said.

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