One person is dead after an engine exploded on a Southwest Airlines flight, sending a piece of shrapnel flying back into a window which caused the woman sitting next to it to be nearly sucked out of the aircraft.

National Transport Safety Bureau Chairman Robert Sumwalt confirmed that one person died on the flight.

READ MORE: Woman who died in horror flight named as mum of two

It is not known if the victim is the same woman who was nearly drawn out of the window when it smashed at 11.15am and who had to be pulled back into her seat by other passengers.

She was taken to hospital immediately after the flight from New York to Dallas made an emergency landing at Philadelphia International Airport at 11.27am local time.

What a flight! Made it!! Still here!! #southwest #flight1380 pic.twitter.com/Cx2mqoXVzY

— Joe Marcus (@joeasaprap) April 17, 2018

There were unconfirmed reports from other passengers that someone suffered a heart attack on the plane and died.

The woman in a critical condition was taken to hospital. Twelve others were assessed and seven of them had minor injuries.

Marty Martinez, left, Facebooked the unfolding drama. (Photo / Marty Martinez)

The Boeing 737-700 was travelling at 32,500ft when the engine on the left side of the plane exploded.

Passengers said they heard a loud 'boom' and the plane immediately dropped, they said, by what felt like 100ft. The woman sitting next to the smashed window was drawn towards it and others next to her held her down for 12 minutes until the plane landed.

Before the NTSB's announcement that there was one fatality involved, the Philadelphia Fire Commissioner said she was taken to hospital in a critical condition.

'One passenger, a woman, was partially drawn out towards the out of the plane, she was pulled back in by other passengers,' Todd Bauer, the father of another passenger on board, told NBC 10.

Terrified passengers shared videos and photos from on board before the plane landed as they descended at 3,000ft per minute until they levelled out at 10,000ft.

The female pilot, named by passengers as Tammy Jo Shults, called air traffic control and asked for paramedics to meet them, saying: 'We have a part of the aircraft missing.'

Asked if the plane was on fire, she said: 'No, it's not on fire but part of it's missing. They said there is a hole and someone went out.'

One passenger filmed himself as he fitted his oxygen mask. 'Something is wrong with our plane! It appears we are going down!

'Emergency landing!! Southwest flight from NYC to Dallas!!' Marty Martinez said as he broadcast live from the plane on Facebook.

He paid $8 to connect to WiFi as the plane was going down, he said, in order to say his goodbyes.

He is the passenger who later told CBS the woman's injuries left 'blood everywhere.' There were confused reports from other passengers that someone on board suffered a heart attack.

Martinez added that the plane 'smelled like ash' once the window was open. He said flight attendants rushed over in shock and pleaded with passengers to cover up the hole.

The first sign of trouble was a loud noise which happened when the engine exploded.

Timothy Bourman, 37, was sitting at the back of the plane when he said he heard a loud 'boom'.

'All the sudden, it felt like we dropped 100 feet. Everybody knew something's going on.

"This is bad, like really bad." A lot of people started panicking and yelling, just real scared.

'We were kind of out of control for a while. It seemed like the pilot was having a hard time controlling the plane. Honestly I think we just all thought we were going down,' he told Philly.com.

Bourman, who was traveling with his wife, said they thought they were about to die until the pilot managed to gain control of the aircraft.

'We're just all really thankful to be alive right now. Thankful to God, thankful to that pilot,' he added.

Matt Tranchin was sitting three rows behind the window that smashed.

He described the chaos and said even the flight attendants were crying in fear.

'Flight attendants rushed up. There was momentary chaos. Everyone kind of descended on where this hole was. As passengers we weren't sure if they were trying to cover up the hole, but the plane smelled like smoke.

Some of the crew couldn't hold back their horror... some were crying as they looked through the open window and onto the engine
'There was ash coming through the ventilation system. We started dropping,' he told ABC News.

'As kind of an indication of how terrifying it was, some of the crew couldn't hold back their horror.

'And some were crying as they looked out through the open window onto the engine,' he added.

As the plane made its descent towards Philadelphia, the crew warned passengers to brace for impact.

Southwest Airlines has not acknowledged the woman's injuries.

In a statement it put out on Twitter, the airline said: 'Southwest Airlines flight 1380, which departed LaGuardia for Dallas Love Field , diverted to PHL because of an operational event.

'The plane landed safely. No slides were deployed.'

It has given no further comment on the injured woman or what caused the engine to explode.

The scene among the passengers. (Photo / Marty Martinez)

When the shrapnel pierced the window, it depressurised the cabin and triggered the oxygen masks. Despite the chaos in the air, others said the emergency landing was fairly calm and smooth.

One passenger told CNN: 'It was a stable landing. We started descending, made the turn back to Philadelphia.

'We were with one engine for maybe 10 minutes.

'We decreased altitude from 8,000 to 5,000 and then when we finally landed it was relatively smooth, kind of a typical landing so the crew and the pilots did a fantastic job.'

Passengers were taken from buses to the airport. It is not the first time the malfunction has occurred on a Southwest-operated Boeing 737-700.

In August last year, a different flight from New Orleans to Orlando was forced to make an emergency landing at Pensacola Airport in Florida after the casing surrounding one of its engines tore away at a similar altitude.

On Tuesday, the airline manufacturer said it was aware of the accident and was prepared to cooperate with investigations.

'Boeing is aware of an incident with Southwest Airlines flight #1380.

'We are gathering more information and stand ready to provide technical assistance,' it tweeted.

The engine which exploded is a CFM56 turbofan engine which costs $10million and has a fan diameter of 68 inches.

The engines are the most popular engines on single aisle commercial planes and are used by all of Airbus A320 aircraft.