Gaza protest as Biden jabs Trump in election-year roast

US President Joe Biden has delivered an election-year roast at the annual White House Correspondents' Association dinner as protesters outside criticised his support for Israel's war against Hamas.

Biden used the annual black-tie event to chide his Republican rival Donald Trump for immaturity, poke fun at his own advanced age and take on the Washington press corps.

"Yes, age is an issue," Biden said.

"I'm a grown man, running against a six-year-old."

"Age is the only thing we have in common," Biden, 81, later added of former President Trump, 77.

"My vice president actually endorses me."

Trump reacted to the event by calling it "really bad" in a post on his Truth Social platform.

"Crooked Joe was an absolute disaster," he said.

"Doesn't get much worse than this."

Demonstrators holding banners outside the gathering at the Washington Hilton chanted about journalists' deaths in Gaza.

Hundreds of protesters encouraged journalists to boycott the annual event and shouted down administration officials as they entered.

Biden avoided the large protests at the front of the hotel by arriving through a back entrance, where he was greeted by smaller groups of protesters calling for a ceasefire.

At the century-old event, often referred to as Washington's "nerd prom", hundreds of journalists, politicians and celebrities rubbed elbows in a massive banquet hall.

It often features friendly jabs from the president in a closing speech that takes aim at reporters and other guests in the audience.

Biden offered some advice to the press corps.

"I'm sincerely not asking you to take sides," he said.

"I'm asking you to rise up to the seriousness of the moment.

"Move past the horse race numbers and the gotcha moments and the distractions, the sideshows that have come to dominate and sensationalise our politics, and focus on what's actually at stake."

This year, the event was hosted by Saturday Night Live cast member Colin Jost.

Grassroots movement CODEPINK marched to the venue from a nearby park.

"The United States media perpetuates anti-Palestinian narratives and ignores Israeli war crimes," the group said on its website.

A growing movement against the war in Gaza has dogged Biden this year including at a $US250 ($A380)-per-ticket March fundraiser at New York's Radio City Music Hall that was disrupted by protesters.

Recently, that movement has expanded to college campuses in the US, signifying a growing revolt inside the Democratic base that Biden needs to defeat Trump, who is now the Republican frontrunner.

Kelly O'Donnell, president of the White House Correspondents' Association, declined to comment on security measures for the dinner.

"The safety and security of our protectees is the US Secret Service's top priority," US Secret Service spokesperson Alexi Worley said, declining to comment further.

Israel's six-month-old war against Hamas in Gaza in response to the October 7 attack by the militant group in southern Israel has killed more than 34,000 people, Palestinian health authorities say, and caused a humanitarian disaster for the enclave's more than two million inhabitants.

The Hamas attack killed 1200 people in Israel and led to 253 being taken hostage, according to Israeli tallies.

The White House Correspondents Association was founded in 1914 and has held a dinner almost every year since 1921 to celebrate the reporters who cover the presidency and raise money for scholarships.