More than 15 years after the terror attacks of 9/11, a cross has been raised on the roof of the only church destroyed when the two planes crashed into the Twin Towers in 2001.

The St. Nicholas Greek Orthodox Church and National Shrine held a "topping out" ceremony on Monday, the Greek Orthodox Archdiocese of America reports.

The traditional ceremony marks the raising of the highest structural element during a project – in this case, a temporary cross that will be replaced with a permanent one when the building work to replace the church is complete.

Archbishop Demetrios of America blessed the cross using holy water in addition to water taken from the National September 11 Memorial & Museum pools.

He said: "We look around today we see the triumph of human spirit and human mind that can overcome any tragedy. Saint Nicholas will offer us the presence of God in our lives and in our city. Here, at this spot, we raise the Cross, which is a symbol of sacrifice and victory, and we offer prayers for the continued construction process."

"Many people walk around the World Trade Centre and wonder about the structure being built and many don't know how it was the only religious site destroyed on 9/11," Jerry Dimitriou, executive director of the Greek Orthodox Archdiocese of America, told the New York Post.

The cross is a "symbol of hope", he added, "it's a symbol of resurrection – that we are rebuilding. And we hope that the when the church opens, it will be that same symbol of hope and reconciliation and understanding."

President Obama gave a major address in Athens earlier this month where he echoed the sentiment that the church was a symbol of hope for America.

"And if anyone seeks an example of our shared spirit, our resilience, they need look no further than New York City, near Ground Zero, where the Greek Orthodox Church of Saint Nicholas, once in ruins, is now rising again," he said.

Work began to rebuild the church in 2014, when Archbishop Demetrios recalled walking through the church after it was destroyed by rubble from the fallen towers.

"We remember this very place filled with ruins, hiding under piles of debris, the pulverised remains of 3,000 innocent victims," he said during the ground-breaking ceremony, according to the Huffington Post.

"Breathing a very heavy air, saturated with the dust of storm, wood, iron and with tiny particles of human bodies, we remember walking with heavy hearts to the specific place where our St. Nicholas stood as a building... The church was not there. We stood there frozen, paralysed, and cried."