Mr Trump also withdrew the United States from the Paris climate accord and the World Health Organisation and threatened huge trade tariffs on neighbouring Canada and Mexico in a whirlwind return to the White House.
The Republican said in a speech after taking the oath at the Capitol — in a ceremony held indoors due to freezing weather — that "America’s decline is over" after four years of Joe Biden’s presidency.
"The golden age of America begins right now. From this day forward our country will flourish and be respected again all over the world," Mr Trump said.
But after the pomp and ceremony it was the showman Trump of his first term — along with the sometimes strongman-style rhetoric — who was on display later in the day.
"Could you imagine Biden doing this? I don’t think so," Mr Trump told a cheering crowd at a Washington sports arena as he threw them the pens he had used to sign a first round of orders.
Mr Trump, 78, then made his triumphant return to the White House, four years after leaving in disgrace, to complete the most remarkable comeback in US political history.
He also signed orders declaring a national emergency at the Mexican border and said he would deploy US troops to tackle illegal immigration — a key campaign issue that drove his election victory over Kamala Harris.
Mr Trump also vowed to "drill, baby, drill" for oil, and scrap rules aimed at persuading motorists to buy electric vehicles.
Finally he vowed to "plant the Stars and Stripes" on Mars.
Mr McCarrigan had travelled to the United States specifically to attend the inauguration, but after the ceremony was moved indoors due to the temperature dropping as low as -10°C he decided to watch it on television in a bar.
Even then it took about two and a-half hours to get there and involved being searched by Secret Service and National Guardsmen as part of a "mind-boggling military exercise", Mr McCarrigan said.
"I wouldn’t want to do it every weekend, but that’s just the price you pay for the event."
The inauguration was a "wonderful occasion" that not many New Zealanders would get to experience, he said.
"Forget about whose side you’re on — it’s quite an epic event to come to."
Mr McCarrigan, who owns the Duke of Wellington pub in Dunedin, said he had always liked Mr Trump and described himself as a conservative voter.
During his inauguration speech, Mr Trump claimed it was an American who split the atom — when it was in fact New Zealander Sir Ernest Rutherford.
He previously made the same claim during a speech at Mt Rushmore in 2020.
Mr McCarrigan said he noticed the remark "straight away", but believed the President was coming at it from an angle of nuclear development.
He "couldn’t care less" that New Zealand was not mentioned and said people needed to get over themselves.
"If that’s what people want to get hung up about back home, it just defies my belief."
Despite needing to be up at 2.45am to catch a three and a-half hour train ride from New York to Washington DC, Mr McCarrigan said the day was "quite the adventure" and "a complete eye-opener".
"We might think going to a big All Black test is big, and it is big, but the scale of the security — it’s just an event that must be just years in the planning.
"Glad I was here, glad I came, I’m glad Dunedin doesn’t get that cold though."
Mr Trump is the first President in more than a century to win a second term after losing an election and the first felon to occupy the White House. The oldest president ever to be sworn in, he is backed by Republican majorities in both chambers of Congress. — AFP & Tim Scott
