An off-duty pilot has been charged with 83 counts of attempted murder, after he allegedly tried to crash a passenger jet during a flight on Sunday night.

The suspect was sitting in the cockpit of an Alaska Airlines flight behind the captain and the first-officer, according to an airline statement.

A police booking document named the suspect as Joseph David Emerson, 44.

The flight was on its way from Everett, Washington, to San Francisco, California, with 80 passengers aboard.

It was diverted to Portland, Oregon, and the suspect was subdued without incident, officials said.

In a statement, Alaska Airlines said the off-duty pilot was traveling in the flight deck jump seat, when he "unsuccessfully attempted to disrupt the operation of the engines."

Crew members on Alaska Airlines Flight 2059 reported the incident to air traffic control.

In a recording of air traffic control communication, one of the pilots was heard saying: "We've got the guy that tried to shut the engines down out of the cockpit, and he doesn't sound like he's causing any issue in the back right now."

"I think he's subdued," the pilot added. He requested police presence "as soon as we get on the ground and parked".

The flight, operated by Horizon Air, was scheduled to take off at 17:25 local time and arrive in San Francisco at 19:30.

However, the flight was diverted to Portland and eventually took off from there to its intended destination at 19:18.

Passenger Aubrey Gavello told ABC News that those on board did not know anything was wrong with the flight until the flight attendant announced that the plane needed to land immediately, later citing a medical emergency.

Ms Gavello told the outlet she heard a flight attendant tell the suspect: "We're going to be fine, it's OK, we'll get you off the plane."

"So I really thought it was a serious medical emergency," she said.

Another passenger told the outlet the situation was handled professionally and passengers were not aware of the crisis.

In a statement, Alaska Airlines said all passengers on board were able to travel on a later flight.

"We are grateful for the professional handling of the situation by the Horizon flight crew and appreciate our guests' calm and patience throughout this event," the airline added.

The incident is now being investigated by the Port of Portland Police Department and the FBI, Alaska Airlines said.

In a statement, the FBI confirmed it was investigating and said it "can assure the traveling public there is no continuing threat related to this incident".

In addition to the attempted murder charges, Mr Emerson also faces 83 counts of reckless endangerment and one count of endangering an aircraft. He was lodged at Multnomah County Detention Center while the investigation continues.

Officials said they were unsure when he would be arraigned.

On Monday, the Federal Aviation Administration sent guidance to US air carriers that the incident was "not connected in any way shape or form to current world events".