Nearly 40 people were injured when a United Airlines flight jolted while flying from Nigeria to the USA. Passengers were feasting on their in-flight meals and settling down to watch a film when the Boeing 787-8 made an ‘unexpected movement’ in the early hours of Friday.

A United Airlines jet was forced to make an emergency landing after plummeting mid-air following take-off. At least six people were injured after the plane jolted during the flight from Nigeria on Friday. The flight, which was heading from Lagos to Washington DC, had 245 passengers and 11 crew on board at the time.

It is unclear what caused the jolt; United Airlines has said the cause was not severe turbulence, and that it is “working with aviation authorities in the US and Nigeria to understand the cause.”

Flight data from Flightradar24 shows that the plane abruptly dropped speed twice during the flight.

A United Airlines flight bound for Puerto Rico made an emergency landing at Newark Liberty International Airport on Saturday morning, according to the FAA. The flight returned to Newark around 10 a.m.