An investigation is underway after a fire broke out on a Staten Island Ferry Thursday evening, forcing nearly 600 passengers on the boat to evacuate, officials said.

At around 5:18 p.m., the FDNY responded to a call for a fire in the mechanical room on a ferry that was traveling from Manhattan to Staten Island.

The city Department of Transportation said the fire was limited to the boat’s engine room.

According to Frank Lieb, a citywide tour commander for the FDNY, the crew had already put CO2 into the engine “as policy” before help arrived.

“Upon arrival, our main objective was to secure the vessel and to start getting the victims, well the passengers, off loaded onto other boats,” he said at a press conference Thursday night. 

The ferry was anchored, and passengers were removed by other boats and brought to the St. George Ferry Terminal on Staten Island, according to the FDNY.

Lieb added that a decision was made to use other ferries to put passengers on instead of fire or police boats because it “was a safer alternative.”

There were a total of five minor injuries, he said, and three people were transported to a local hospital.

Lieb said the fire is currently under control and they will wait a minimum of 24 hours to determine if they can open the engine hold to ensure that the fire is extinguished. 

According to NY Waterway, who assisted with the evacuation, 558 passengers were evacuated.

The Marine Engineers' Beneficial Association, the Staten Island Ferry’s union, called Thursday’s fire “very alarming.”

“We have been deeply concerned about the safety of our passengers and crew as the new Ollis vessels have had serious issues and the DOT failed to train our members on the new fleet,” MEBA said in a statement.

“It is time for the Mayor and NYCDOT to work with us to hear our staffing and safety concerns,” the union continued.

Staten Island Borough President Vito J. Fossella credited the ferry crew for their "professionalism," but questioned how the fire occurred in the first place.

"The Staten Island Ferry is a lifeline for tens of thousands of Staten Island commuters and others," Fossella said in a statement. "While we don't want to jump to conclusions, there needs to be a thorough review of the safety of this ferry and the other two Ollis-class boats."