NEW YORK - President Barack Obama hosted the first Leaders Summit on Refugees in New York City on Tuesday, saying the world is facing a crisis of epic proportions.

"We are here because right now in crowded camps in cities around the world there are families from Darfur in Chad, Palestinians in Lebanon, Afghans in Pakistan, Colombians in Ecuador, who’ve endured years, in some cases, decades, as refugees surviving on rations and aid and who dream of someday, somehow, having a home of their own,” the president said.

Syrian refugee Yusra Mardini, a member of the refugee Olympic team, introduced Obama. She told her family’s story, saying they were refugees on a boat, and that when the engine failed, she and others had to get out and pull the boat by swimming.

?Just a year later, Mardini said, she had the chance to compete in the Rio Olympics on the refugee team. She offered this message: “It is not a choice to flee from your home. ... Refugees can achieve great things if given the opportunity.”

Yusra Mardini, a swimming for the Refugee Olympic
Yusra Mardini, a swimming for the Refugee Olympic Team, speaks during the Leaders Summit on Refugees during the 71st session of the United Nations General Assembly at UN headquarters, Sept. 20, 2016.

Praise for Syrian refugee, olympian

Obama told Mardini he could not be prouder of her, "for your courage and your resilience and the great example that you're setting for children everywhere — including your 8-year-old sister, who I know must look up to you.”  He said she was the face of so many young girls and boys who have had to flee their homes.

The president said the worst global refugee crisis since World War II is a test of the international community’s ability to stop conflicts. He said so many of the world’s refugees come from three countries ravaged by war: Syria, Afghanistan and Somalia. Obama said the global refugee crisis poses a security threat because of its enormous scale.

“When nations with their own internal difficulties find themselves hosting massive refugee populations for years on end, it can risk more instability,” he said.

But the president implicitly rejected criticism by Republican presidential nominee Donald Trump and Republican leaders in Congress.

Many Republican leaders have called for a halt to the admission of refugees from Iraq, Syria and other countries embroiled in conflict, saying they pose a security threat. The president said the U.S. has one of the world’s most exhaustive vetting procedures in place for would-be refugees.

In this photo taken on Sept. 13, 2016, a Kurd Syri
In this photo taken on Sept. 13, 2016, a Kurd Syrian mother gives cough syrup to her child at Ritsona refugee camp north of Athens.

Test of humanity

Obama said he believed the refugee crisis was a test of the world’s common humanity, adding that people simply could not avert their eyes from displaced families.

“To slam the door in the face of these families would betray our deepest values," he said. "It would deny our own heritage as nations, including the United States of America, that have been built by immigrants and refugees. And it would be to ignore a teaching at the heart of so many faiths that we do unto others as we would have them do unto us.

?Obama was joined in hosting the summit by U.N. Secretary-General Ban Ki-moon and leaders from Canada, Ethiopia, Germany, Jordan, Mexico and Sweden.

Companies pledge help

Earlier Tuesday, the White House announced that 51 private U.S. companies had pledged to invest $650 million to help refugees around the world.

The companies include Airbnb, IBM, Twitter, Facebook, Google, Chobani, Uber, Ikea and Microsoft. They have vowed to provide various types of in-kind support to refugees, including Chromebook computers from Google, plus educational, job training and employment opportunities.

Obama had issued a call to action to government agencies, other world leaders and private companies to join together to make a difference in the lives of refugees.

Ban also paid tribute to Mardini, saying she might not have won a medal at the Olympics but was a winner nonetheless. He called on world leaders to show their compassion to the 21 million people across the world like Mardini who are classified as refugees, asking, "If not us, then who can do it?"