Smoke could be seen wafting out of a window from an upper floor earlier, the staff member said.
Several people in high-vis were seen redirecting ferry passengers away from the terminal entry.
Two fire trucks arrived 30 minutes after the building was first evacuated, from the west Auckland stations of Waitakere and Laingholm, along with two police cars.
An aerial platform was being used to reach the building’s fourth storey.
Ferry passengers could be seen waiting idly outside the downtown Ferry Building while Fire and Emergency staff entered. A fourth fire truck arrived at the scene around 1.15pm.
A crowd of around 100 people has gathered at the bottom of the Intercontinental Hotel to watch.
Auckland Transport said it was aware of the fire, but because the fire was in the building and not the wharf, there were no disruptions to ferry services at this stage.
Members of the New Zealand Professional Firefighters Union (NZPFU) have been conducting hour-long rolling strikes of pay since August. Industrial action was escalated this month with two lunchtime strikes a week.
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