At least seven people died after a UPS cargo plane crashed in a fireball during takeoff from Louisville, Kentucky, on Tuesday night. The Louisville airport, which is home to UPS Worldport – a global hub for the shipping company’s air cargo operations and its largest package-handling facility worldwide – was expected to reopen on Wednesday morning. Two runways were strewn with debris from the crash.

In a Tuesday night service alert, UPS said delivery schedules 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,” it added.

The triple-engine plane was fueled for an 8-1/2 hour flight to Honolulu. It had a crew of three, UPS said. None survived, officials said.

Louisville Mayor Craig Greenberg told reporters at a late-night news briefing that four deaths were confirmed on the ground, with 11 injured people taken to hospitals. Separately, Kentucky Governor Andy Beshear said the death toll was at least seven and expected to rise. Some survivors had suffered “very significant” injuries, he said.

It was the first UPS cargo plane to crash since August 2013, when an Airbus aircraft went down on a landing approach to the international airport in Birmingham, Alabama, killing both crew.

Television channel WLKY, a CBS affiliate, showed video of Tuesday’s crash, with flames visible as the plane took off, and the fireball erupting as it hit the ground. Several buildings in an industrial area beyond the runway were on fire after the crash, with thick, black smoke seen rising into the evening sky. Beshear said stricken facilities on the ground included a petroleum recycling center and an auto parts business.

“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 for investigators is why one engine appeared to have separated from the plane before the crash, a person briefed on the matter said, pointing to video images of airfield debris. The cause and origin of the fire before the aircraft went down were also unknown.

U.S. air safety expert and pilot John Cox said investigators will need to look at why the plane with three engines failed to fly after one apparently 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 on the ground burned for hours afterwards, with authorities warning the public within a 5-mile (8-km) radius of the scene to stay indoors to guard against air-quality hazards. The shelter-in-place zone was later reduced to a mile across.

FAA records show the crashed plane, an MD-11 freighter, was 34 years old. Boeing, which shut down the MD-11 program after acquiring it in a merger with McDonnell Douglas, said it was concerned for the safety and well-being of 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. It climbed to an altitude of 175 feet and reached a speed of 184 knots before making a sharp descent, Flightradar24 data showed.

The National Transportation Safety Board will lead the accident investigation and was sending a team to the site, a spokesperson said. The NTSB typically takes 12 to 24 months to complete an investigation, make a finding of probable cause and issue recommendations to help avoid similar incidents.

UPS is the largest employer in Louisville, providing 26,000 jobs, the publication Louisville Business First said. “We are terribly saddened by the accident tonight in Louisville,” the company said in a statement.

Louisville’s Worldport is at the center of the hub-and-spoke system for its air cargo network, serving the high-tech, healthcare and retail industries, handling more than 300 flights and processing about 2 million packages a day. More than 150 UPS customers, such as Merck & Co and other major pharmaceutical companies, have inventory there.

“My heart goes out to everybody at UPS, because this is a UPS town,” Louisville Metro Council member Betsy Ruhe, whose district includes the airport, said at the press conference. “We all know somebody who works at UPS, and they’re all texting their friends, their family, trying to make sure everyone is safe. Sadly, some of those texts are probably going to go unanswered.”