President Barack Obama greeted Pope Francis when he began the U.S. leg of his tour in the Americas as the pontiff who is known for his teachings on the poor arrived in the world's biggest economy.

The Pope will visit Washington DC, New York, where he will address the United Nations, and Philadelphia after his trip to Cuba.

"I've never said anything that is not in the social doctrine of the church," the Pope told reporters. "Maybe I have given the impression of (being) a bit lefty, but that would be a mistaken interpretation."

Francis landed at Andrews Air Force Base near Washington DC with Obama and his family greeting him along with Vice-President Joe Biden, the first Catholic vice-president who was there with his wife.

The U.S. stars and stripes and gold and white Vatican flags fluttered from the cockpit windows of the Pope's Italian plane as it taxied toward black red clad clerics and children from local Catholic schools, CNN reported.

There was a military honor guard, schoolchildren, politicians, and Roman Catholic clergy to great the first Latin American pontiff and the fourth pope to visit the United States after his visit to Cuba.

Pope Francis arrived in the United States with both Catholic and non-Catholic Americans showing they have a favourable view of the world's iconic Christian leader.

A new Rasmussen Reports poll of 1,000 Americans has Pope Francis' total approval rating at 60 per cent, half of which viewed him "very favourably," Catholic News Agency reported the day before his scheduled arrival in Washington.

The rating is even higher among American Catholics, who gave him a 78 per cent approval rating, 48 per cent of which reporting a "very favorable" view.

Sixty-five percent of U.S. Catholics said the Pope has been good for the Church, compared to just 15 percent who believe he's had a negative impact.

The impressive rating makes him the envy of the less favorably viewed, including Obama, Donald Trump, and, well, most other political figures at this time, said CNA.