The fire broke out around 12:30 a.m. on the Upper East Side.
Most patients were told to stay in their rooms as firefighters put out the blaze.
Twenty patients were briefly moved from their rooms to another floor as firefighters quickly put out the flames.
Employees and others were ushered outside.
It apparently started as an electrical fire in a sub-cellar generator room.
Four people were checked out at the scene.
Madison Avenue from 97th Street to 102nd Street was closed for FDNY activity, but reopened later Friday morning.
Mount Sinai released a statement saying, "Mount Sinai Health System confirmed today at approximately 12:30 am that a fire broke out in the generator room of the Annenberg Building at The Mount Sinai Hospital. Twenty patients were transported to unaffected areas of The Mount Sinai Hospital. No injuries were reported. Mount Sinai Health System would like to express our sincerest gratitude to front line staff and FDNY first responders."
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