Firefighters are still working to put out a fire that erupted on a Hoegh Autoliners car carrier off Jacksonville, Florida, almost 21 hours ago, according to emergency responders.

The fire broke out shortly before 1600 hours local time on Thursday after an explosion occurred on the seventh deck of the 4,900-ceu Hoegh Xiamen (built 2010).

The ship had taken on about 2,000 vehicles at Blount Island Marine Terminal shortly before the explosion.

"This is still an active incident, with many vagaries still attached to the ongoing suppression activity that preclude any definitive statements from being provided until such time as the operation has been terminated," Jacksonville Fire and Rescue Department spokesman Tom Francis told TradeWinds.

The fire department is on the scene trying to extinguish the fire, with assistance from the Jacksonville Sheriff's Office, Blount Island Port Authority and US Coast Guard detachment in Jacksonville.

"The Coast Guard is monitoring the vessel for any pollution or environmental impact and making sure the vessel remains intact," Petty Officer 2nd Class Ryan Dickinson told TradeWinds.

The incident has not impacted the natural environment and the ship is maintaining structural integrity, Dickinson said, but a 500-yard safety zone and oil boom have been placed around the vessel as a precaution.

Hoegh Autoliners has confirmed in the latest update on its website that none of the 21 crew members taken off the ship were injured as a result of the incident.

"Hoegh Autoliners has activated its emergency response team and is working closely with all necessary authorities to contain the incident," the company said.

"Our priorities at this time are to secure the vessel and ensure the preservation of the local environment."

Eight injured firefighters were taken to the hospital, four being sent to Shands Gainesville burn unit for serious burns.