By Mike Segar

NEWARK, NEW JERSEY (Reuters) -Two New Jersey firefighters were killed and five injured while battling an intense blaze overnight on a cargo ship packed with hundreds of vehicles docked at Port Newark, officials said on Thursday.

The Italian-flagged Grande Costa d’Avorio was carrying 1,200 new and used vehicles when a fire broke out on its 10th deck at about 10:30 p.m. EST (0330 GMT) on Wednesday, vessel operator Grimaldi Deep Sea said in a statement.

As members of the Newark Fire Department responded, the blaze quickly spread to the 11th and 12th levels, Chief Rufus Jackson said during a news conference.

Firefighters battling the blaze were pushed back by the intense heat, he said.

"Two firefighters were lost while backing out. Searches were initially made to recover the two firefighters and we were unable to do so," Jackson said, adding numerous rescue crews were called to the scene.

The firefighters killed in the blaze were identified as Wayne Brooks Jr., 49, and Augusto Acabou, 45. Five other firefighters suffered smoke and burn injuries and were taken to a hospital, fire officials said.

"This is not a common fire for the city of Newark and the Newark firefighters," Jackson said. "It's a different type of fire, and they're still willing to put themselves on the line."

Aerial footage from local media on Thursday morning showed a firefighting vessel dousing an upper floor of the cargo ship with water as smoke rose from several torched vehicles.

Port Newark, near New York City, is under jurisdiction of the Port Authority of New York and New Jersey. It is among the largest U.S. ports and among the busiest on the Eastern seaboard.

It was unclear how the fire started, Grimaldi Deep Sea said, adding no fuel spill had been detected at sea and the stability of the ship does not appear to have been compromised.

The ship, which had 28 crew members aboard, was carrying cars, vans and rolling equipment as well as 157 shipping containers. There were no electric cars or hazardous cargo aboard, the company said.

(Additional reporting by Brendan O'Brien and Rami Ayyub; Editing by Hugh Lawson, Mark Porter and David Gregorio)