A medical jet with six Mexican nationals on board crashed into a busy Philadelphia neighbourhood on Friday, authorities said, marking another US aviation disaster after a passenger plane and a military helicopter collided mid-air in Washington earlier this week.

Video footage appeared to show the twin-engine plane descending at a sharp angle towards a residential area, sparking a huge fireball upon impact and showering wreckage over homes and vehicles.

The Federal Aviation Administration (FAA) said the aircraft was a Learjet 55 – an American-French business jet – that had taken off shortly before from Northeast Philadelphia Airport bound for Branson, Missouri.

The crash happened just after 6:00 pm (2300 GMT).

A young girl who had been in the United States for medical care, her mother, and members of the flight and medical crews accompanying her on board were killed in the crash, said the children's hospital that had treated her.

"The patient had received care from Shriners Children's Philadelphia and was being transported back to her home country in Mexico on a contracted air ambulance when the crash happened," said Mel Bower, a spokesman for Shriners Children's.

All six of those on board were Mexican citizens, the country's foreign ministry said in a statement.

"The airline company... confirmed to the consulate that six people of Mexican nationality were travelling on the aircraft," the ministry wrote on X.

The operator, Jet Rescue Air Ambulance, confirmed in a statement to US media that there were two passengers and four crew, adding, "At this time, we cannot confirm any survivors."

Dozens of emergency workers were on the scene outside Roosevelt Mall, a strip mall in Northeast Philadelphia with retailers and food outlets.

US President Donald Trump posted on Friday on his Truth Social platform that he was "sad" to see "more souls lost" in the Philadelphia tragedy. He praised first responders, adding: "God Bless you all."

Witnesses told local TV crews that they saw body parts in or near the wreckage, as Philadelphia City Council member Mike Driscoll said he feared residents or others on the ground may have been killed.

"It doesn't look good. And it's a sad situation here," he told CNN.

The FAA said it was launching an investigation with the National Transportation Safety Board. (AFP)