Flames from the crash, which occurred shortly before sundown, ignited a string of fires on the ground in an industrial corridor adjacent to the airport, forcing authorities to halt airport operations through the night, according to officials.

The Louisville airport, which is home to UPS Worldport - a global hub for shipping company's air cargo operations and its largest package-handling facility worldwide - was expected to reopen on Wednesday morning. Debris from the crash was left strewn across two runways.

UPS said in a Tuesday night service alert that its scheduled delivery times for airborne and international packages "may be affected" by the disruption.

"Contingency plans are in place to help ensure that shipments arrive at their final destinations as quickly as conditions permit," the company said.

The triple-engine plane was fueled for an 8-1/2 hour flight to Honolulu. The aircraft carried a crew of three, according to UPS UPS.N. Officials later said none had survived.

Louisville Mayor Craig Greenberg told reporters at a late-night news briefing that four fatalities were confirmed on the ground, and 11 other people who were injured had been taken to hospitals.

Separately, Kentucky Governor Andy Beshear said the overall number of lives lost was at least seven, with the death toll expected to rise. He said earlier that some of the survivors had suffered "very significant" injuries.

Television channel WLKY, a CBS affiliate, showed video of the crash as it occurred. Fire on one wing was visible in the video as the plane took off, and a fireball erupted as it hit the ground. Several buildings in an industrial area beyond the runway were on fire after the crash, with thick black smoke rising into the evening sky. 

"UPS Flight 2976 crashed around 5:15 p.m. local time on Tuesday, Nov. 4, after departing from Louisville Muhammad Ali International Airport in Kentucky," the Federal Aviation Administration said in a statement.

One key question investigators will look at is why one engine appeared to have separated from the plane before the crash, a person briefed on the matter said, noting video reports of debris on the airfield. The cause of the fire was also unknown.

US air safety expert and pilot John Cox said investigators will need to look at why the plane with three engines failed to fly after the first one caught fire.

“It’s too big a fire for a normal, typical-engine fire,” Cox said. “It’s much too big.”

“That airplane should have flown on two engines. So now we’ve got to look at what caused it not to fly,” he added.

Fires were still burning near the airport, Louisville Mayor Craig Greenberg said in a social media post shortly before 7 p.m. ET (0000 GMT). 

Officials issued a shelter-in-place order for all locations within 5 miles (8 km) of the airport.

FAA records show the plane involved in the crash, an MD-11 freighter, was 34 years old. Boeing, which shut down the MD-11 program after acquiring it in its merger with McDonnell Douglas, said it was concerned for the safety and well-being of all those affected, and it would provide technical support to the investigation.

Flightradar24 said the plane, which began operations with UPS in 2006, had flown from Louisville to Baltimore earlier on Tuesday before returning to Louisville. The flight from Louisville to Honolulu typically takes 8-1/2 hours, the flight tracking service said.

The aircraft climbed to an altitude of 175 feet and reached a speed of 184 knots before making a sharp descent, according to data from Flightradar24. 

UPS said it had yet to confirm any injuries or casualties due to the accident.