Pope Francis has become the first pontiff to address a joint meeting of the US Congress, where he received a warm welcome from more than 500 lawmakers, justices and officials.

He was greeted at the US Capitol by Speaker of the House John Boehner, who is Catholic, and then entered the chamber to thunderous applause.

His speech repeated his opposition to the death penalty and abortion.

And he emphasised the importance of welcoming immigrants.

He said the world is facing a refugee crisis of a magnitude not seen since World War Two, and noted that thousands travel north into the US for a better life every year.

"We must not be taken aback by their numbers, but rather view them as persons, seeing their faces and listening to their stories, trying to respond as best we can to their situation," he said.

After finishing with the words "God bless America", he received a prolonged standing ovation.

Thousands of people have gathered on the West Lawn of the Capitol hoping to see the 78-year-old Argentine pontiff.

Sitting behind him was Vice President Joe Biden and Mr Boehner, the first and second in line to the presidency, who are both Roman Catholics.