Passengers on a US flight looked out of their windows to find that large parts of the plane's engine had fallen off.

The incident happened on board Southwest flight 3472 from New Orleans to Orlando.

The plane's captain made the decision to divert the flight to Pensacola, where it landed without injury to the 99 passengers and five crew.

A spokesman for Southwest said the flight had experienced a "mechanical issue with the number one engine".

The airline added that the plane remains out of service and it was working get passengers to their destinations as soon as possible.

Another passenger told KOCO-5 of Oklahoma City that she had been on the flight with her husband and their three children.

She said the plane was over water when she heard a "big explosion".

A great job today by our professional @SouthwestAir pilots! The best safety device is always a well-trained pilot. pic.twitter.com/B4GpLyC6gA

— SWA Pilots' Assn. (@swapapilots) August 27, 2016

"There was some smoke and then nothing. I saw parts flapping in the wind because it was right outside my window."

She said the plane - which landed at 9.40am on Saturday local time - began to shake, descend rapidly and oxygen masks fell.

"I held my kids, and one was freaking out, crying. And so, we're trying to hold his hand and singing and praying a lot," she said.

"It wasn't until after I got on the ground that I got emotional."

The plane was steadied before one of the pilots told passengers that one of the engines had been lost.

The woman praised the crew for their professionalism and added that "it was thanks to the pilot that we're all alive".

An investigation into the incident has been launched by the National Transportation Safety Board in the US.