A small medical transport plane has crashed into several buildings in northeast Philadelphia, setting homes and vehicles ablaze and injuring people on the ground.

The jet was on a medical transport mission on Friday evening and carrying four crew members, a child patient and the patient's escort, Jet Rescue Air Ambulance, a medical aircraft company, said in a statement.

"We know that there will be a loss," Pennsylvania Gov Josh Shapiro said during a news conference at the scene of the crash, calling it an "awful aviation disaster".

Emergency crews rushed to the evening crash scene as residents crowded streets littered with fiery debris and pieces of the aircraft.

Witnesses described a chaotic scene with people who were injured and structures ablaze.

The child on board the plane was receiving care in the US for a life-threatening condition and was returning to Tijuana, Mexico, Shai Gold, a spokesman for Jet Rescue Air Ambulance, told a local NBC outlet.

The girl was accompanied by her mother, a pilot, a copilot, a doctor and a paramedic, the spokesman said.

Mr Gold told NBC the child's treatment was sponsored by a third-partner charity.

"She fought quite a lot to survive, and unfortunately, this tragedy on the way home," he said.

The Mexican Consulate in Philadelphia put out a notice on X for Mexican nationals affected by the incident to call a helpline.

Philadelphia Mayor Cherelle Parker said city officials do not know the number of fatalities, but the city is "asking for prayers for anyone and everyone that may have been affected".

"If you see debris, call 911, don't touch anything," she told city residents.

The crash happened just blocks from the Roosevelt Mall, a three-storey shopping centre in a densely populated part of Philadelphia, the fifth biggest city in the US.

The area where the crash occurred is filled with terraced housing and shops.

Videos of the incident online show the plane coming down quickly and sparking a huge fireball.

Witnesses described shrapnel from the crash damaging cars and sending burning debris into the streets. Photos of the aftermath show burning cars mangled.

One man who spoke with CBS, the BBC's US partner, said he was driving in the area when he heard a whirring sound and then a loud explosion.

"Everyone just started screaming," he said.

One witness told local media that the explosion "lit up the whole sky".

"I just saw a plane basically hit the building and it exploded. The sky lit up and I pulled over and basically, it was just real bad around here," the witness told WPVI-TV, describing the crash as feeling like an earthquake.

Ryan Tian, 23, told The Philadelphia Inquirer he was getting dinner when he saw a "massive fireball" that turned the sky orange.

"I thought we were getting attacked by something," he said. As he saw people start to flee, he decided to get "outta there".

What do we know about the crash?

The plane, a Learjet 55, took off from the Northeast Philadelphia Airport at about 18:30 local time and crashed less than four miles (6.4km) away, according to the Federal Aviation Administration (FAA).

The FAA said in a statement that the flight was en route to Springfield-Branson National Airport in Missouri. At first, the agency said two people were on the plane but later revised that to six.

According to data on FlightAware, a flight tracking website, the plane was operated by a company called Med Jets and had arrived in Philadelphia from Florida less than four hours earlier.

The FAA and National Transportation Safety Board (NTSB) are investigating.

In a statement, President Donald Trump said his administration was "totally engaged".

"So sad to see the plane go down in Philadelphia, Pennsylvania. More innocent souls lost," he said.

The plane crash comes just two days after a much larger collision happened between a commercial jet and a military helicopter in Washington DC, where officials suspect all 67 people aboard both aircraft were killed.

It was the deadliest plane crash in the US in over 20 years.