Pope Francis has decried what he called a polarising surge in much of the world to exclude people with different nationalities, races or beliefs as enemies, as he led a ceremony welcoming 17 new cardinals from six continents.

The consistory ceremony in St Peter's Basilica formally inducted the churchmen into the cardinals' ranks.

One of the new "princes of the church," as the cardinals are sometimes called, an 87-year-old bishop from Lesotho, Africa, was too frail to attend the ceremony; his red hat will be delivered to him, the pope announced in Latin.

Francis used his homily to encourage the new crop of cardinals to be near to, not remote from, the flocks of faithful they will lead.

He said love is needed for "the conversion of our pitiful hearts that tend to judge, divide, oppose and condemn", and cautioned sombrely against those who "raise walls, build barriers and label."

Little more than a week after Donald Trump was elected the next US president, the pope noted "how quickly those among us with the status of the stranger, an immigrant, or a refugee, become a threat, take on the status of an enemy.

"An enemy because they come from a distant country or have different customs. An enemy because of the colour of their skin, their language or their social class. An enemy because they think differently or even have a different faith," he said at a ceremony to induct new cardinals.

One of the new cardinals, Archbishop Blase Cupich of Chicago, said the pope was "very much aware of the fact that if that (animosity) is not checked, it is very contagious and it can spread quickly, it can be like a wildfire".

In his homily, the pope said the Church itself was not immune to "a virus of polarisation and animosity", an apparent reference to a public challenge by four conservative cardinals, who accused him of sowing confusion on moral issues. 

Popes, in selecting cardinals, look for men who share their approach to the church's mission in the world.

Among the newly made cardinals is Indianapolis Archbishop Joseph Tobin, who defied the governor of the US state of Indiana, Mike Pence, by welcoming Syrian refugees. Cardinal Tobin in January will become archbishop of Newark, New Jersey; Mr Pence will be installed as vice president of the United States.

17 new cardinals were inducted during today's ceremony. Photo: Reuters

The new cardinals who pledged loyalty to the pope on Saturday included prelates from Africa, Asia, Europe, Oceania, and North and South America.

Some of their homelands include Papua New Guinea, Mauritius, Malaysia, Venezuela, Mexico, Bangladesh and Brazil.

One of them, an 88-year-old Albanian priest, Ernest Simoni, personally knew the suffering caused by hatred. Cardinal Simoni spent 18 years in prison because of his faith, facing both solitary confinement and hard labour, in his homeland during its communist regime.

Since cardinals are usually bishops already, Francis bestowed a rare honour on giving that rank to Cardinal Simoni, a simple priest. After Cardinal Simoni kneeled before Francis to receive his red hat, he clasped the pope's hand tightly and seemed to fight back tears.

When Francis visited Albania in 2014, he was brought to tears after the then Father Simoni told him how he was persecuted. Cardinal Simoni, who worked to reconcile feuds in many of that country's villages, after decades of serving clandestinely as a priest until the country's communist rule ended in 1990.

Another new cardinal, Italian Archbishop Mario Zenari, is the pope's envoy to Syria. Greeting Francis on behalf of all the 17 prelates, Cardinal Zenari recalled war-torn countries, places where "the unlucky, adults and children, (are) left for dead, or half-dead on the streets of their villages and neighbourhoods, or under the rubble of their homes and schools, because of the brutal violence and bloody, inhuman and inextricable conflicts there".

Archbishop Dieudonne Nzapalainga, of Bangui, Central African Republic, also was among the fresh crop of cardinals. In 2015, Francis visited Cardinal Nzapalainga's country, bloodied by sectarian violence between Christian and Muslim militants that has forced more than one million people to flee their homes.

The two other new cardinals from the United States are Chicago Archbishop Blase Cupich and Archbishop Kevin Farrell, who served as bishop of Dallas before Francis appointed him to head the Vatican office for laity, family and life issues.

Thirteen of the 17 new cardinals are under 80 years old and thus eligible to vote in a secret conclave for the next pope.

Francis has now appointed 44 of the 120 cardinals young enough to elect his successor. The others were named by the previous two pontiffs, John Paul II, whom Francis made a saint, and Benedict XVI, who retired in 2013.

After the basilica ceremony, the new cardinals and the pope were taking two mini-buses to the monastery on Vatican grounds where Benedict lives so they can greet the emeritus pontiff, the Vatican said.