PHILADELPHIA, Feb 2, (AP): A person in a car was the seventh fatal victim of the fiery crash of an air ambulance onto a busy Philadelphia street, authorities said Saturday, as investigators sifted through burned cars, damaged homes and charred debris for clues to determine why the aircraft plummeted shortly after takeoff. Carrying six people from Mexico, including a child who spent months in treatment at a hospital, the Learjet 55 went down just after departing from the Northeast Philadelphia Airport, creating what witnesses described as a massive fireball, shaking houses and leaving a chaotic street scene.

Authorities couldn't yet say why the jet crashed, and Adam Thiel, the city’s managing director, said it could be days - or longer - until officials are able to fully count the number of dead and injured across a sprawling impact area in a densely populated residential area. The plane took off, reached about 1,500 feet of altitude and then plummeted in a steep descent, crashing less than a minute after takeoff in what National Transportation Safety Board chair Jennifer Homendy called a "high-impact crash” that left the plane "highly fragmented.”

As of Saturday morning, officials said, there were seven dead - six on the jet and the person in the car - and 19 injured. Most of the injured had been treated and released, hospitals said. There are "a lot of unknowns about who was where on the streets” when the plane crashed, and it is possible that the casualty figures will grow, Thiel said.

The crash scene was at least four to six blocks, and authorities were working to assess the damage, including going house to house to inspect the dwellings, Thiel said. Homendy said her agency’s staff was working to collect debris from the plane, which could take days or weeks, and haul it away to a secure location to begin evaluating it.

Air traffic controllers didn't hear anything concerning before the crash, and her agency was still looking for the cockpit voice recorder, a helpful piece of evidence in the investigation, Homendy said. It is likely damaged and possibly fragmented because of the impact, although her agency's researchers and engineers have significant expertise in repairing them, she said. The plane hit the ground just after 6 p.m., during a busy Friday evening dinner hour less than 3 miles (5 kilometers) from the airport.