Prominent Washington journalists, if not Hollywood stars, celebrated the First Amendment during the annual White House Correspondents' dinner, an event that lacked the glitter of past years because of the absence of the president of the United States.

With President Donald Trump sending his regrets, the attention was no longer focused on an in-person roasting of the commander in chief and his humorous remarks about politics and the press. The red carpet that once featured Oscar winners, TV stars and a few major-league athletes barely turned heads.

Instead, speakers at the dinner promoted press freedom and responsibility and challenged Trump's accusations of dishonest reporting.

White House Correspondents' Association president Jeff Mason counters Trump's media claims 1:25

The stars of the night were Watergate reporters Bob Woodward and Carl Bernstein, who recounted what they learned about journalism from their reporting for The Washington Post that helped lead to President Richard Nixon's resignation more than 40 years ago.

"Like politicians and presidents sometimes, perhaps too frequently, we make mistakes and go too far," Woodward said. "When that happens we should own up to it. But the effort today to get this best obtainable version of the truth is largely made in good faith. Mr. President, the media is not 'fake news."'

Watergate reporters Bob Woodward, centre, and Carl Bernstein, right, approach the podium as White House Correspondents' President Jeff Mason looks on. (Cliff Owen/Associated Press)

The evening was not without humour aimed at the press and Trump.

"We've got to address the elephant that's not in the room," cracked the entertainment headliner, Hasan Minhaj of The Daily Show on TV's Comedy Central. "The leader of our country is not here. And that's because he lives in Moscow. It's a very long flight. As for the other guy, I think he's in Pennsylvania because he can't take a joke."

Trump was indeed in Pennsylvania, having scheduled a rally in Harrisburg to mark his 100th day in office. He began his remarks with a lengthy if familiar attack on the news media while dismissing the dinner and its participants.

"A large group of Hollywood actors and Washington media are consoling each other in a hotel ballroom in our nation's capital right now," Trump said. He added: "And I could not possibly be more thrilled than to be more than 100 miles away from Washington's swamp, spending my evening with all of you and with a much, much larger crowd and much better people, right?"

U.S. President Donald Trump speaks at a rally in Harrisburg, Pa., on Saturday, the same night as the dinner. (Carolyn Kaster/Associated Press)

Trump became the first president since Ronald Reagan in 1981 to skip the event — and Reagan was recovering from an assassination attempt.

The official WHCA dinner began in 1921. In recent decades, the event offered Washington's press corps an opportunity to wear black tie and stunning gowns while mixing with celebrity guests. Most people trace that development to 1987, when Baltimore Sun reporter Michael Kelly brought Fawn Hall, the secretary at the centre of the Iran-Contra affair.

Jeff Mason, the WHCA president, said before the event that this year's dinner would have been different even if Trump had attended, "based on the tension that has existed in the relationship and some of the things he has said about the press. We were preparing for a different dinner, either way."

The correspondents' dinner was briefly upstaged Saturday afternoon when late-night TV star Samantha Bee of Full Frontal pulled in celebrities for the first Not the White House Correspondents' Dinner, among them Alysia Reiner of Orange Is the New Black, Retta of Parks and Recreation and Matt Walsh of Veep.

Bee's taped show, a tongue-in-cheek tribute to American news organizations, featured actor Will Ferrell and other guests roasting Trump and his allies. It singled out the Committee to Protect Journalists, the non-profit group that will receive proceeds from the broadcast.