Be alert for street closures this afternoon around St. Patrick’s Catholic Church in downtown Washington.

The church is holding its 17th Annual Blue Mass for first responders from across the country. The event began at 12:10 p.m.

According to the church Web site, “we pray for those in law enforcement and fire safety, remember those who have fallen, and support those who serve.”

Hundreds of officers and safety officials line up outside for a procession into the church, which is located in the 600 block of 10th Street NW, at the corner of 10th and G. The officers pass under an American flag suspended from fire ladder trucks.