A delta airliner experiencing mechanical problems on Tuesday dumped jet fuel onto a school playground in the Los Angeles area, leaving 20 students and several adults with minor injuries.

Delta Flight 89 took off from Los Angeles en route to Shanghai and was forced to turn back due to engine trouble, the airline’s spokesperson said.

The plane landed safely around noon after dumping its fuel, which fell onto a wide area, including Park Avenue Elementary School, located about 25km east of the airport.

Fire officials said about 20 children and 11 adults complaining of skin irritation or minor respiratory problems at the elementary school were treated on the spot and did not require hospitalisation.

In a statement, a Delta spokesperson said the fuel was released to allow the plane to land safely.

“Shortly after takeoff, Flight 89 from LAX to Shanghai experienced an engine issue requiring the aircraft to return quickly to LAX,” Adrian Gee said in the statement.

“The aircraft landed safely after a release of fuel, which was required as part of normal procedure to reach a safe landing weight. “We are in touch with Los Angeles World Airports and the LA County Fire Department and share concerns regarding reporting minor injuries to adults and children at a school in the area,” he said.

The fuel also landed on other schools in south Los Angeles but there were no injuries among students or staff, authorities said.

In a statement, the Los Angeles Unified School District said students and staff were in the playground of the elementary school when the incident happened.

They “may have been sprayed by fuel or inhaled fumes”, it said, adding that school officials “immediately called paramedics, who are on the scene and are treating anyone who is complaining of skin irritation or breathing problems”.

“I was so scared. We went inside and then my eyes started itching,” Marian Torres, an 11-year-old student, told CBS News.

Justin Guiti, a fifth-grader at Park Avenue who was hit by the fuel told CNN that it sprayed all over him and his friends, getting into his eyes. “Drops of water were coming down. I thought it was a rainbow and I looked up, and it was gasoline.”

Miguel Cervantes, a sixth-grader who was also hit told CNN that his skin was itchy afterwards. “I thought it was smoke. But when it went down, I felt it and it smelled like gas.”

The Federal Aviation Administration said it was investigating the incident and said there are special fuel-dumping procedures for aircraft operating into and out of major US airports.

“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,” the agency said in a statement.

Later on Tuesday after inspecting all the affected schools, hazardous materials experts said there was no more danger, CNN reported. All schools will be open and operating on their normal schedules on Wednesday.

“With the monitoring devices that we have, there are no explosive limits that are being detected at all, as well as solid or liquid products remaining,” Battalion Chief Jason Robertson said as quoted by CNN, adding that the fire department believes all of the jet fuel has evaporated.

A former Boeing 777 captain expressed his surprise at the pilots’ actions, telling CBS News that the pilots had enough time to safely circle and dump the fuel over water at a higher altitude, which he estimated was between 55,000 and 75,000 litres.