An unknown odor briefly sickened a dozen parishioners at a Gwinnett County church early Sunday, authorities said.

Firefighters responded to a call and found 12 people outside the Pilgrims Mission International Church in the 4200 block of Pleasant Hill Road in Duluth about 2:30 a.m., Gwinnett County fire Capt. Tommy Rutledge said.

The people, who were participating in a choir rehearsal, had headaches that quickly went away once they were outside, he said. Paramedics checked them out at the scene, and no one was taken to a hospital.

The fire department's hazardous materials team checked the church twice and found no problems.  The odor was no longer present, and crews were unable to identify it or locate a source, Rutledge said.

Authorities left the scene just before 4 a.m.