VATICAN CITY (AP, AFP) - Pope Francis celebrated his first Easter Sunday Mass as pontiff in St. Peter's Square, packed by joyous pilgrims, tourists and Romans and bedecked by spring flowers.

Wearing cream-coloured vestments, Francis strode onto the esplanade in front of St. Peter's Basilica and took his place at an altar set up under a white canopy.

Speaking in front of some 250,000 people from around the world in the Vatican, Francis prayed for "dear Syria, for its people torn by conflict and for the many refugees who await help and comfort. "How much blood has been shed! And how much suffering must there still be before a political solution to the crisis will be found?" he said.

"On the Korean peninsula, may disagreements be overcome and a renewed spirit of reconciliation grow," he said, a day after North Korea declared it was in a "state of war" with South Korea.

Latin America's first pontiff also issued an appeal for hostages held by militants in Nigeria and condemned human trafficking as "the most extensive form of slavery in this 21st century".

Faithful had already filled the square hours before the Mass began in mid-morning, and throughout the service streams of people kept flocking there for his speech and blessing, traditionally delivered after the Mass from the central balcony of the basilica.

By mid-ceremony, some 250,000 people had turned out, the Vatican said.

Francis bowed his head in reflection as the Gospel was sung in Latin, recounting what Christians believe is the central mystery of their faith - the resurrection of Jesus after this death by crucifixion.

After heavy rain battered Rome during the night, more was forecast. But Sunday saw sunny skies alternate with clouds.

With Rome's chilly, rainy winter postponing the blossoming of many flowers until recently, the square was a welcome riot of floral color in the city. Sprays of yellow forsythia and daffodils and white lilies - the colors of the Vatican flag - dominated, but there were also bursts of lavender and pink, from potted azalea, rhododendron, wisteria and other plants.

Pope's Easter speech has been used by past pontiffs to reflect on the world's conflicts and ills.

Since Francis was elected pope on March 13, becoming the first Latin American and first Jesuit pontiff ever, he has put concern for the poor and others on the margins of society at the heart of his attention to set an example for his flock.