A Los Angeles-bound Alaska Airlines flight was forced to return to Seattle's airport Monday afternoon after an airport worker fell asleep and became trapped in the cargo hold.

Alaska Airlines said the flight had taken off from Seattle-Tacoma International Airport at 2:39 p.m. local time. Fourteen minutes later, the plane's captain and some first-class passengers heard banging coming from beneath the aircraft. The pilot decided to return to the airport and declared an emergency for priority landing.

"I think we’re hearing a noise from the baggage compartment," the pilot said, according to KCPQ. "Might be a person in there, so we’re going to have to come back around."

After the plane landed a ramp agent came out from the front cargo hold, which Alaska said is pressurized and temperature-controlled. The area is often where animals are kept during flights. 

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

The man, an employee of Alaska contractor Menzies Aviation, walked off the plane. He was initially checked by medics at the airport and found to be unhurt, airport spokesman Perry Cooper said.

The man was also checked at a hospital and released, the airline said Monday evening. After his release from the hospital, he passed a drug test, airline spokesman Bryan Zidar said.

The airline did not identify the worker. A Menzies spokesman did not immediately return an email request for comment and details about the employee.

Alaska Airlines said the man started work at 5 a.m. Monday and was due off at 2:30 p.m.. He had been part of a four-person team loading baggage onto the flight.

Before the plane departed, the leader of the man's team noticed he was missing, called into the cargo hold for him and called and texted the man's cellphone but got no answer, the airline said. Co-workers thought he had finished his shift and gone home.

The Federal Aviation Administration is investigating the incident, spokesman Allen Kenitzer confirmed in an e-mail. 

All ramp employees undergo full criminal background checks and drug checks before hiring and are subject to random drug tests during their employment, the airline statement said.

The plane carried 170 passengers and six crew members.

The flight departed again at 3:52 p.m. and arrived at a terminal gate in Los Angeles at 6:29 p.m., more than an hour late, the airline said.

The Associated Press contributed to this report.