UPDATE: An official from the Port Authority now tells The Huffington Post that there was zero evidence of a blaze on the 88th floor and that the reported fire was a false alarm.

This is the second such false alarm in the past four months. In April, a novelty hand grenade delivered to Two World Financial Center caused the evacuation of the building.

EARLIER: A fire broke out early Wednesday morning on the 88th floor One World Trade Center, fire department officials said.

84 firefighters from 26 units are responding to the blaze which began at 7:42 AM.

No one was inside the skyscraper-- now New York City's tallest-- when the fire erupted.

The cause of the fire is unknown, fire officials told NBC New York.

For live video of the blaze, go here.

This is a developing story...