The death toll from the crash of a medical jet carrying a Mexican child home from a hospital in Philadelphia has risen to seven, officials said Saturday, with 19 others wounded.

The crash — the second major aviation disaster in the United States this week — occurred Friday when the twin-engine Learjet 55 plummeted towards a busy Philadelphia neighborhood, exploding on impact and showering wreckage over homes and vehicles.

Officials had earlier said that all six on board — a young girl who had been in the United States for medical care, her mother, and members of the flight and medical crews with her — were killed. They were all Mexican nationals.

On Saturday, Philadelphia Mayor Cherelle Parker said that at least one other person, who was in a car, had also been killed, and that 19 people had been wounded.

Speaking at a press conference, Parker warned that the toll was "not etched in stone" and could yet rise. 

"We have a lot of unknowns about who was where on the streets of this neighborhood last night at the time of impact," said the city's managing director Adam Thiel, warning that it could be days before the full toll emerged. 

He said the impact area covered four to six blocks, and there was also debris in a "remote area where something happened with the aircraft."

Mexican President Claudia Sheinbaum posted her condolences on social media platform X. 

The US Federal Aviation Authority (FAA) said it was launching an investigation with the National Transportation Safety Board.

Both agencies are already probing the deadliest US air disaster in almost a quarter century, after a passenger jet operated by an American Airlines subsidiary collided with a Black Hawk helicopter on Wednesday.

The airliner with 64 people onboard was landing at Reagan National Airport in the Washington area — just miles from the White House — when it collided with a US Army helicopter on a training mission.