The NYPD and federal law enforcement agencies took part in an active shooter drill on Sunday.

The exercise is supposed to prepare authorities for potential incidents, like last week's attacks in Paris. The drill took place in a Manhattan subway station.

U.S. Secretary of Homeland Security Jeh Johnson said the public will be safe this holiday season.

"We encourage Americans as the holiday season approaches to continue to travel ... to go to public places as the holiday season approaches. And let's remember that terrorism cannot prevail if the people refuse to be terrorized," Johnson said.