The first Mass began at 7 a.m. but crowds of people flocked there overnight for the annual Christmas tradition, celebrating Midnight Mass.
Timothy Cardinal Dolan reminded worshippers of the true meaning of the holiday.
On Christmas Eve, hundreds of parishioners packed St. Paul's Chapel in Lower Manhattan for their annual children's service, just one of many religious celebrations around New York City.
The soothing sounds of the choir resonated in the chapel, as children and their parents lined the pews for the Christmas Eve Family Eucharist.
Officials called it a simple service with families in mind, featuring traditional Christmas carols, a children's sermon, giant puppets telling the story of the Nativity, and the Trinity Youth Chorus.
There is no incense at this service.
Midnight Masses are always popular, and as usual, there is stepped up security around places like St. Patrick's Cathedral.
Officials say there are no credible threats, but they are beefing up patrols out of an abundance of caution.
Christmas Mass is a holiday tradition for many families, and most have grown accustomed to the sight of heavily-armed officers.
Crowds faced long security lines for Masses, but the NYPD insists the goal is to keep the holiday about the holiday and that they treat all denominations equally.
People lined up an hour in advance to take part in the Christmas Eve mass at St. Patrick's Cathedral.
They came from all of the world, including Chile, France and Ireland.
"Saint Patrick is a big, really really well known in Ireland so I think it will be interesting to go back home and explain to a friend the experience," said Marine Stevenson, who is visiting Manhattan from Ireland.
While people marked their seats long before the service, dozens of officers and their cars lined the streets surrounding Fifth Avenue to make sure it's a peaceful celebration.
It's not just visitors taking part in the service. Many locals have made it a part of their annual tradition.
"I love the rich history and how everybody from all over gets together for the celebration of Christmas," said Kody Barton of New Jersey.
It's a celebration under a century old roof where inside, visitors say, they get away from the Fifth Avenue store fronts and experience what the holiday is really about.
"There's not a better time to spend just a few minutes to reflect on that and make sure our kids can understand what the spirit of that is and find ways to serve and that's why we're here today," said visitor Brett Nielson.
The 5:30 Mass was first come first serve. The Christmas Eve Midnight Mass is for ticket holders only.
So many showed up for the earlier Mass the line literally wrapped along Fifth Avenue, as people patiently waited just to get a glimpse of the inside.
Security increased dramatically Tuesday night as police cleared everyone from all of the surrounding side streets and blocked them off to traffic, to ensure a safe night for everyone.
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