The South Wing was evacuated for hours because of problems inside a mechanical room.
Steam poured through vents and into the terminal area.
Many people thought the place was filling with smoke.
"The alarm system was going off for like an hour. Actually more than an hour it was going off. It was very annoying and when they told us to leave we were all confused," said store worker Deedat.
The Port Authority says the leak was traced back to ConEd equipment.
The impact to travelers was minimal because buses were re-routed to the North Wing.
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