Nine people remain missing after a UPS plane departing Louisville Muhammad Ali International Airport in Kentucky on Tuesday crashed in a ball of flames, killing at least 12 people. Officials continue to search through half a mile of “charred, mangled” debris to find any additional victims, authorities said.

“It’s been a long 36 hours of tragedy,” Louisville Mayor Craig Greenberg said at a press conference on Thursday.

UPS Flight 2976 crashed around 5:15 p.m. local time on Tuesday, according to the Federal Aviation Administration. The McDonnell Douglas MD-11 freighter plane was headed to Daniel K. Inouye International Airport in Honolulu, when the plane’s left engine detached after a “large plume of fire” erupted from the plane’s left wing, according to the National Transportation Safety Board.

The NTSB said it located the “main component of the engine” on Thursday.

The aircraft’s three crew members are believed to be among the dead, Greenberg said.

UPS identified the pilots on board the flight as Capt. Richard Wartenberg, First Officer Lee Truitt and International Relief Officer Capt. Dana Diamond.

“Words can’t express the sorrow we feel over the heartbreaking Flight 2976 accident,” Nando Cesarone, the UPS executive vice president for U.S. and UPS Airlines, said in a statement on Thursday. “Our hearts go out to every UPSer who has been impacted and all in our Louisville community — supporting you and ensuring you receive the care and resources you need is our priority.”

The coroner is working on identifying the other nine victims who were found, Greenberg added.

Authorities will now begin to move the debris, including the “charred, mangled metal,” to see if they can locate additional individuals, Greenberg said.

The nine missing individuals are believed to have been near the scene at the time of the crash, Greenberg said.

“Our hope is that we have located all the victims at this point, but we don’t know,” Greenberg said.

Two individuals who were hospitalized still remain in critical condition, Kentucky Gov. Andy Beshear said on Wednesday.

On Thursday, the NTSB said the data from the black boxes was downloaded, which the NTSB said was a “good extraction.”

A probable cause of the crash has not been revealed, the NTSB said.

“The plane lifted off and gained enough altitude to clear the fence at the end of runway 17R. Shortly after clearing that fence, it made impact with structures and the terrain off of the airport property,” according to NTSB board member Todd Inman.

Preliminary flight data reveals the aircraft’s last reported altitude was 475 feet, the NTSB said on Thursday.

Prior to the crash, the aircraft was in San Antonio for six weeks, with the NTSB saying they will “look at every piece of maintenance that was done” during that time.

The plane did not require any maintenance the day of the crash, Inman said on Thursday.

The NTSB did not reveal when a preliminary report on the crash would be released.

Video captured the moment the plane — loaded with thousands of gallons of fuel for a long-distance flight to Hawaii — crashed, resulting in a large fireball.

Two businesses on the ground were impacted by the crash, Beshear said.

The FBI, the Environmental Protection Agency and the Bureau of Alcohol, Tobacco, Firearms and Explosives are now assisting in the investigation, Greenberg said.

ABC News’ Sam Sweeney contributed to this report.