Nearly 40 people were injured when a Boeing 787-800 plane suddenly lost altitude during a United Airlines flight from Lagos, Nigeria, to Washington, D.C., early Friday, officials said.

The U.S. National Transportation Safety Board (NTSB) is investigating a United Airlines flight incident that led to passenger and crew injuries following a sudden aircraft movement. The flight, en route from Lagos to Washington D.

The authorities in Nigeria said that the United Airlines plane had to return to Lagos, Nigeria, after the episode. Six people were treated at a hospital, officials said.

In an update, Nigerian officials said an additional 27 passengers and 5 crew members suffered minor injuries in the incident. In all, 38 were hurt.

Dozens of passengers sustained injuries after a Washington-bound United Airlines flight made an emergency return to Lagos for "technical" reasons.

A United Airlines flight, a Boeing 787-8 outbound from Lagos to Washington Dulles, on Thursday, declared an emergency and made an air return to Lagos.

A United Airlines flight UA613, outbound from Murtala Muhammed International Airport, Lagos,  declared an emergency and returned to

United Airlines flight UA613, travelling from Lagos to Washington, US. experienced a mid-flight emergency and returned.

The same United Airlines aircraft had a similar issue earlier this week, with a rapid altitude drop prompting a diversion.

Six were injured on a United Airlines flight from Lagos to Washington after the plane had a technical issue that caused an "unexpected movement."

After diverting, United Airlines Flight UA613 landed safely back in Nigeria. Four passengers and two flight attendants were taken to hospital with injuries but have been discharged, United Airlines said in a statement. The Federal Airports Authority of Nigeria (FAAN) said an additional 27 passengers and five crew members sustained minor injuries.