An airliner with engine trouble dumped jet fuel that fell as a smelly mist on dozens of schoolchildren while the plane made an emergency return to Los Angeles International Airport, officials said.

The fuel, described by fire officials as a vapor, caused minor skin and lung irritation to 56 children and adults but nobody was taken to the hospital and the only decontamination required was soap and water, officials said.

Delta Air Lines Flight 89 to Shanghai reported an engine problem only minutes after takeoff.

"Delta 89, heavy, we have engine compressor stalls on the right engine," the pilot reported to air traffic control, according to a recording of the radio conversation.

A stall, which can be caused by damage to a turbine, either from a malfunction or sometimes by a bird striking the engine, reduces the engine thrust.

The pilot was asked whether he wanted to keep the aircraft over the ocean to dump fuel but declined, although it appears he may have changed his mind later about whether the plane could safely land weighing as much as it did.

The fuel sprayed out of the plane in two lines and descended at midday in the city of Cudahy and nearby parts of Los Angeles County, about 21 kilometres east of the airport.

"The mist fell on five elementary schools, but all injuries were minor and there weren't any evacuations," Los Angeles County Fire Department Inspector Sky Cornell said.

"That's a great sign. All the fuel evaporated very quickly and nothing flammable remained in the air or on the ground," he said.

Diego Martinez, a sixth grader at Park Avenue Elementary in Cuday, said he and his classmates were outside for physical education class when they saw the airplane flying low overhead.

"It was very close."

Shortly afterward, the air filled with the pungent odor of fuel.

"It was very strong, the odor," the 12-year-old said. Diego wasn't doused but some of his friends complained that their skin was itching.

"Some teachers at Park Avenue had headaches from the smell," said Antonio Buenabad, area representative for the United Teachers Los Angeles union.

"They were anxious to get home and shower because the stench was very strong," he said of the teachers.

Delta Air Lines said the aircraft landed safely after releasing fuel, which was required as part of normal procedure to reach a safe landing weight.

”The FlightAware website's flight track showed the jet took off over the ocean and made an immediate right turn toward land and circled back over Southern California to approach the airport from the east."

The Federal Aviation Administration said it is investigating.

"There are special fuel dumping procedures for aircraft operating into and out of any major US airport,” the FAA said in a statement.

"These procedures call for fuel to be dumped over designated unpopulated areas, typically at higher altitudes so the fuel atomises and disperses before it reaches the ground. However, pilots can deviate from the rules in an emergency for safety reasons," said Doug Moss, a retired airline captain and owner of AeroPacific Consulting, LLC, an aviation consulting firm based in Reno, Nevada.

"The pilot could have stayed over the ocean to dump his fuel but that could have taken thirty minutes up to an hour," Moss said.

Moss said when there is a compressor stall, the crew can't determine how much damage was done internally to the engine.

"The fan blades may have separated and cut into the fuel lines, leaving an uncontrollable fire as a future possibility,” Moss said.

"He's flying an airplane with a damaged engine that may be on fire,” Moss said. "So he has to make the decision: Do I spend the time to dump fuel or do I put this thing on the ground as soon as I can? You're not going to kill anyone by dumping fuel."

"There's no dereliction of duty. Everybody's trying to do the best they can but it's a fast-paced, dynamic ballgame and there's not a lot of time to think [...] lives are at stake,” Moss said.

"He got it on the ground safely. Unfortunately, there was collateral damage. People got gas poured over them."

Cornell said 31 children and adults were affected by the fuel dump at Park Avenue school and another 12 at 93rd Street Elementary school. The rest of those affected were at other schools.