U.S. President Donald Trump on Saturday issued a scathing attack on the national news media at a Pennsylvania rally he organized for the same evening the White House Correspondents' Association hosts its annual dinner.

To cheers in Harrisburg, Pa., he accused the news media of "fake news" and said if their job was to be honest and tell the truth, then they deserved "a big, fat failing grade."

He said that in contrast, his administration has been delivering for the American people every day.

Trump also said the media is trapped at the dinner in Washington and he predicted it will be "very, very boring."

"I could not possibly be more thrilled than to be more than 100 miles way from Washington's swamp," he said, "spending my evening with all of you and with a much, much larger crowd and much better people, right?"

Saturday's rally offered a familiar recapitulation of what Trump and aides have argued for days are administration successes, including the successful nomination of Neil Gorsuch to the Supreme Court, his cabinet choices and the approval of construction of the Keystone XL pipeline.

Trump's 100th day events were set in politically important Pennsylvania, which he won with 48 per cent. It was the first time the state had voted for a Republican presidential candidate since George H.W. Bush in 1988.

Trump also signed an executive order directing the Commerce Department and the U.S. trade representative to conduct a study of U.S. trade agreements.

The goal is to determine whether the U.S. is being treated fairly by its trading partners and the 164-nation World Trade Organization.

Trump 'very happy' with 1st 100 days

Trump's 100-day rally was a bit of counter-programming from the former reality television star.

Back in Washington, media organizations and a few stars were gathering on Saturday for the annual White House Correspondents Association Dinner.

Trump, who has derided journalists as "dishonest" and even enemies of the American people, is the first president since 1981 to stay away from the event. That year, Ronald Reagan was recovering from an assassination attempt.

Trump's first 100 days: By the numbers0:49

At the 100-day mark, Trump chose instead to spend the evening with people who helped elect him and, polls show, remain largely in his corner. Though the White House created a website touting its accomplishments of the first 100 days, Trump has tried to downplay the importance of the marker, perhaps out of recognition that many of his campaign promises have gone unfulfilled.

"It's a false standard, 100 days," Trump said while signing an executive order on Friday, "but I have to tell you, I don't think anybody has done what we've been able to do in 100 days, so we're very happy."

A failed effort to overhaul president Barack Obama's health care law behind him, Trump is turning to what he's billed as the nation's biggest tax cut. It apparently falls short of Reagan's in 1981, and tax experts are skeptical that the plan would pay for itself, as Treasury Secretary Steve Mnuchin has claimed.

Trump

People walk past a trailer featuring slogans in support of Trump as they wait in line to attend his rally in Harrisburg, Pa., on Saturday. (Patrick Semansky/Associated Press)

The economy, so far, has been Trump's ally. Polls show that Americans feel slightly better about his job performance on that subject than his job performance overall.

"Together we are seeing that great achievements are possible when we put American people first," Trump said in his weekly radio and internet address. "That is why I withdrew the United States from the Trans-Pacific Partnership. That day was a turning point for our nation. It put the countries of this world on notice that the sellout of the American worker was over."

He said in his remarks: "In just 14 weeks, my administration has brought profound change to Washington."

Executive orders in line to be signed Saturday would be the 31st and 32nd since Trump took office — the most of any president in his first 100 days since the Second World War. During the campaign, Trump railed against Obama's use of orders, which don't need congressional approval.