NEWARK, N.J. (AP) - Two firefighters were killed battling a blaze that began when cars caught fire deep inside a cargo ship carrying 5,000 cars at a New Jersey port, Newark’s fire chief said Thursday.

Responding firefighters found five to seven vehicles already on fire when they reached the 10th floor of the cargo ship at Port Newark around 9:30 p.m. Wednesday night. The blaze quickly extended to the 11th and 12th floors, and as firefighters were pushed back by the intense heat, two of them were lost, Fire Chief Rufus Jackson said at a news conference.

Firefighters weren’t initially able to find their colleagues and outside rescue companies from around the state were called in. They were found and removed from the structure, but unfortunately they lost their lives, Jackson said.

Marine traffic trackers show the Grande Costa D’Avorio, which was built in 2011, arrived from the Port of Baltimore several days earlier.

“We lost two firefighters today,” said Newark Mayor Ras Baraka at the scene. “A tragedy for us in the city of Newark and tragic for all firefighters who know what it means to go in a burning structure in a danger that you are going to have to experience when you do so.”

Baraka said he saw unparalleled acts of bravery and camaraderie, but he called the loss traumatic for all of Newark. The fire was still burning while officials spoke at the news conference, but they would continue to work to put it out, Baraka said.

Shipboard firefighting is a unique skill and Newark firefighters don’t commonly face this kind of fire, Jackson said.