The largest disaster drill since Sept. 11 at the World Trade Center site is under way.

New York City officials staged a mock explosion on a PATH commuter rail train Sunday morning in the tunnel linking the site to northern New Jersey. Hundreds of police officers, firefighters and Port Authority of New York and New Jersey officials are taking part.

There are also 150 volunteers pretending to be victims of the explosion.

Officials bought TV ads and plastered train stations with posters to warn downtown residents of the drill. They say there haven't been as many responders at ground zero since the Sept. 11 attacks.

PATH rail service is suspended Sunday morning during the drill, reported AP.