Security is expected to be tight, and delays extensive, as President Obama and tens of thousands of people attend the gala opening Saturday of the National Museum of African American History and Culture.

In addition to the president and first lady Michelle Obama, former President George W. Bush and former first lady Laura Bush will join members of Congress, the Supreme Court and visitors from across the country on the Mall.

Museum officials said they expect about 20,000 people to attend the opening and related events.

Streets around the museum, at 14th Street and Constitution Avenue NW in downtown Washington, will be closed, and security access points will be in place.

Parking near the site is prohibited, and visitors are encouraged to use Metro and other public transportation. The nearest Metro stops are Smithsonian and Federal Triangle.

Security will be a “wonderfully collaborative effort with [the] Smithsonian, with the Park Service, with the Secret Service,” Founding Museum Director Lonnie G. Bunch III said last week.

“We recognize that there will be unprecedented crowds and security,” he said. “We feel very comfortable that we’ve got a process in place to handle that.”

The event will pale in terms of crowds beside Obama’s first inauguration in 2009, which drew a record 1.8 million people to the Mall, and for the visit of Pope Francis in September 2015, which produced one of the largest and most complex security cordons attempted in Washington.

Still, Sgt. Anna Rose, a spokeswoman for the U.S. Park Police, which handles security on the Mall, said, “We expect to have quite a few visitors.” She noted that a festival connected to the museum’s opening will have “high attendance.”

Rose said police “at this time . . . do not have any credible threats, and no threats that I know of, period.” She said authorities have been planning security for the event for several months.

The outdoor ceremony begins with a “gathering and musical prelude” at 8 a.m. The dedication of the newest Smithsonian Institution museum is set for 10 a.m. The ceremony will be live-streamed on the Internet at

Among other VIPs, Rep. John Lewis (D-Ga.), a veteran of the civil rights struggle of the 1960s, and Supreme Court Chief Justice John G. Roberts Jr., chancellor of the Smithsonian, are expected to attend the dedication.

The museum opens to the public at 1 p.m. But timed passes are required, and, because of high demand, none are available until November.

The free timed passes for November and December are available through the museum’s website.

On Saturday the public will not be allowed onto the museum grounds, but can watch from the grounds of the Washington Monument and on large television screens.

Visitors will have to go through security screening checkpoints at 17th Street NW, Constitution Avenue NW, 17th Street SW and Independence Avenue SW.

Items prohibited include alcohol, ammunition, pets, balloons, bicycles, fireworks, guns, knives of any type, folding tables, tents, chairs, tripods, glass containers, soda cans, hard-shell coolers, laser pointers, pepper spray, scissors, screwdrivers, razor blades and needles.

Screening and bag checks will also be in place for the free music festival, “Freedom Sounds: A Community Celebration,” on the grounds of the Washington Monument, Friday through Sunday.

Festival entrances also will be at 17th Street and Constitution Avenue NW, and 17th Street and Independence Avenue SW.

On Saturday from 6 to 9 p.m, featured performers include Living Colour, Public Enemy and the Roots. A host of musicians, storytellers and dancers will perform throughout the weekend.

Artifacts from some of the performers — Public Enemy and jazz bassist Stanley Clarke — are on display inside the museum.

Some streets may close from 7 p.m. Friday through 10 p.m. Sunday. They include:

●Both directions of Constitution Avenue from 12th Street NW to 18th Street NW. Traffic will be diverted onto 12th, 17th and 18th streets. The 12th Street tunnel will remain open.

●15th Street from Pennsylvania Avenue NW to Maine Avenue SW.

●14th Street from Pennsylvania Avenue NW to Independence Avenue SW. Access to the Ronald Reagan Building and International Trade Center from 13th Street NW.

●Madison Drive NW from Seventh Street NW to 15th Street NW.

●Jefferson Drive SW from Seventh Street SW to 15th Street SW.