As New York City (search) tightened security in the wake of what authorities called a specific threat against the city's subway system, parts of Penn Station (search) were shut down on Friday after a suspicious package was found.

According to Amtrak supervisor Mike Gallagher, the sections of the station were closed "because of something that was found here." He declined to be more specific.

The item was reportedly found near a ticket counter in the station on the West Side of Manhattan.

Late in the morning emergency workers in hazmat suits were visible working near what appeared to be a red suitcase. Police closed an entrance to the station at 33rd and Eighth Avenue and National Guardsmen were also on the scene.

The New York Police Department (search) said the closures were not affecting train service.

Penn Station is one of Manhattan's busiest transportation hubs.

The Associated Press contributed to this report.