An Amazon cargo plane ran off a runway at Miami International Airport on Sunday, killing at least five people after it struck vehicles and burst into flames, according to authorities.

The aircraft overran the runway at approximately 2 p.m. following its arrival from San Juan, Puerto Rico. Five people were killed, three were critically injured, and two others were hospitalized with less severe injuries, Miami-Dade County officials said at a news conference. Officials said Sunday afternoon that it was too early to determine whether those who died were on board the aircraft or in the vehicles it struck.

The crash sent thick black smoke billowing into the sky. Miami-Dade Rescue Fire Chief Ray Jadallah said the pilot and copilot were trapped in the cockpit, some vehicle occupants were trapped in their cars, and another person was trapped under a vehicle.

The incident halted flights at the busy travel hub for much of the afternoon. Miami International is one of the busiest airports in the United States and a major gateway for Latin American traffic, meaning disruptions there ripple quickly across connecting routes. Several hours after the crash, fire crews were still working to address a fuel leak on the plane, Jadallah said.

Images from the scene showed the Prime Air aircraft came to rest beside a roadway near two semi-trucks. Despite the fire, the plane appeared to be largely intact, resting on its belly.

The flight was operated by 21 Air, a cargo carrier based in North Carolina. Amazon Air, the company's air cargo network, relies on a mix of leased and contractor-operated aircraft rather than flying its own fleet, an arrangement common among integrated freight and e-commerce operators. According to flight-tracking site Flightradar24, the 32-year-old Boeing 767 was originally built as a passenger aircraft and flew for several airlines for more than two decades before being converted to a freighter in 2015. Converted freighters of this kind are a widespread practice in the cargo industry, where older passenger airframes are retrofitted with cargo doors and reinforced floors to extend their service lives.

About 250 flights were delayed at the airport by late Sunday afternoon, according to FlightAware, a website that tracks flight disruptions.

The National Transportation Safety Board said it is sending a team to Miami to investigate, led by Chairwoman Jennifer Homendy. NTSB investigations into runway incidents typically examine factors such as weather conditions, aircraft braking performance, runway surface, landing speed and weight, and typically issue final findings — including any safety recommendations — months to a year or more after the accident.

Amazon said in a statement that it would cooperate with any investigation.

"We're heartbroken to learn that five people lost their lives in today's incident at Miami International Airport," the company said. "Our deepest sympathies go out to the families, loved ones, and all those affected by this devastating loss."

Jackson Lee, who runs an electronics shop near the crash site, went outside with four colleagues after the crash and saw smoke rising near the airport's fences.

"We hear planes taking off and landing every five minutes. I thought I'd got used to it," Lee said. "I never thought it could come this close to us."

This story was originally featured on Fortune.com.