WASHINGTON -- U.S. President Donald Trump gives few news conferences, and when one came Friday it was sudden, unexpected and chaotic.

After making a surprise visit to the White House lawn for a half-hour interview with "Fox & Friends" host Steve Doocy, Trump took 20 minutes of questions from a boisterous group of White House reporters. It was televised live on cable news.

Trump's remarks -- about North Korea, his zero tolerance immigration policy, the investigation into his campaign's ties with Russia -- offered enough fodder for television talkers to chew over all day and into the weekend. No one had any idea it was going to happen an hour before the president emerged.

Doocy, typically New York-based, was in Washington this week to cover the congressional baseball game. He stayed over to help anchor Trump's favourite morning show from the area on the White House grounds where television reporters usually congregate for live shots. No guests were expected; the White House offered a trade representative and Fox turned them down.

Doocy nearly didn't get in; Secret Service officials couldn't find his pass and barred him at the gate. He was sitting on the curb outside the White House at 6:10 a.m., and his colleagues started "Fox & Friends" without him.

At 7:50 a.m., Trump noted on Twitter that the show was at the White House. "Maybe I'll have to take an unannounced trip down to see them?" he tweeted.

Most of the White House press corps hadn't arrived for the day; the administration had said the night before that the president would not be seen in public before 11 a.m. and there were no events on his official schedule. The tweet sent a skeleton crew of reporters, camera crews and photographers scrambling out to the driveway leading to the West Wing, checking with sources whether a presidential appearance was really possible.

Doocy said Fox was tipped that Trump was serious, but no one knew whether it would be more than a hello.

"I was cramming for a test," he said. "I had 30-some minutes to come up with as many interesting questions about things in the news as I could."

When other reporters noticed tourists being escorted away from Pennsylvania Avenue in front of the White House and heard the Secret Service was preventing colleagues from entering the grounds, they knew it was happening. Trump emerged, and the gang of reporters peppered him with questions. He walked to Fox's location followed by a pack of camera crews and journalists, an unusual sight for a president who is usually kept at a distance by security.

One camera operator, walking backwards to capture the unusual Trump appearance, fell to the ground. "It was chaos," said Evan Vucci, a photographer who recorded the scene for The Associated Press.

After 30 minutes talking to Doocy, Trump walked over to where the other reporters were standing to answer more questions. Unlike a planned news conference, where reporters are called upon individually, here reporters frequently shouted all at once until the president focused on one question.

"Quiet!" Trump said at one point, noting about one unidentified reporter, "she's so obnoxious."

The setting, however, forced the journalists to keep their questions brief and to the point: Will you suspend Mueller? Why did you halt military exercises (in Korea)? How can Kim Jong Un love his people if he's killing them? Do you think Pruitt is using his office for private gain? Are you afraid Michael Cohen might flip? Are you planning to meet with Putin?

Maggie Haberman, White House reporter for The New York Times, tweeted that there was "something perfect about Trump attempting to give Fox special treatment on the taxpayers' lawn and getting swarmed by the free press, blowing their exclusive."

Doocy said he didn't mind, that it reassured him that he didn't miss obvious questions in his interview.

Trump has only given two formal White House news conference open to a wide range of reporters and, for much of the past year, has confined the bulk of his on-camera interviews to friendly faces at Fox News Channel.

He's broken out a bit more in recent weeks, delivering a news conference for a small group of travelling reporters at the G-7 summit in Quebec and one lengthy news conference at last week's North Korea summit in Singapore. He has also spoken to reporters on the South Lawn of the White House and with those travelling with him aboard Air Force One and granted a handful of interviews, including with George Stephanopoulos at ABC News.

Bauder reported from New York.