A Los Angeles-bound flight has returned to Seattle after it was discovered a worker had fallen asleep in the cargo hold before take-off.

Fourteen minutes after Alaska Airlines flight 448 took off on Monday, the pilot and passengers in first class heard screaming and banging from beneath the aircraft.

'Help! Help! Help!' the man screamed, according to one passenger.

The airline said in a news release the captain immediately returned to Seattle-Tacoma International and declared an emergency for priority landing.

The cargo hold where the handler was trapped is temperature controlled and pressurized, so he was not in danger of freezing or running out of oxygen.

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This is the moment an Alaska Airlines baggage handler was pulled from the cargo hold after falling asleep

Safe: This is the baggage handler who fell asleep aboard the Alaska Airlines flight from Seattle to Los Angeles on Monday

A passenger on board Flight 448 recorded video of the baggage handlder's knocking that passengers could hear inside the cabin

Emergency landing: The pilot turned back to Seattle 14 minutes into the flight when he heard screaming

'At some point the marshal kind of made himself known and started banging back and he yelled really loud and said, "We're getting ready to land, hold on to something,"' Troi Ge, a passenger on board the flight, told NBC News.

Mr Ge, a sound designer from Burbank, recorded video aboard the plane in which passengers could hear the banging from the cargo hold.

After the plane landed a ramp agent was found inside the front cargo hold.

Video taken by KIRO 7 showed the worker calmly walking out of the cargo hold and putting on a high visibility jacket.

He stood talking to airport staff for a few seconds before walking off towards the terminal.

'Upon exiting, he told authorities he had fallen asleep,' the airline said.

The worker, an employee of Menzies Aviation, walked off the plane and appeared well, but was taken to a hospital as a precaution.

The airline says it is investigating the situation.

The pilot could hear banging and screaming from beneath the aircraft as they flew from Seattle to LA

The man appeared to be well as he walked around the runway talking to airport employees

Alaska Airlines is investigating how the man managed to fall asleep before the LA-bound flight took off

Passenger Marty Collins told KOMO-TV in Seattle the flight was surrounded by emergency vehicles when it returned to the airport.

She said passengers did not hear the worker banging or making noise.

'Nobody on the plane heard anything like that, nobody knew why we were turning around,' she told the station. 'They just said we were fine and we weren't in any danger.'

Passengers were later told about the situation.

'They just said there was someone in the cargo hold and he's been escorted off and taken away,' she said.