All flights into and out of Newark Liberty International Airport in New Jersey were halted Monday morning after air traffic controllers evacuated the tower due to the ingress of smoke from an elevator.

AP reports the Federal Aviation Administration confirmed the closure but would not speculate further on the cause of the invasive fumes or their specific nature.

During the pause, FAA staff relocated to a backup tower at the airport, according to the Port Authority of New York and New Jersey, which operates the airport.

They later returned to the primary tower, the AP report makes clear. It continued:

Earlier this month, four airports serving Washington, D.C., Baltimore and Richmond, Virginia, halted all flights for over an hour because of a strong chemical smell that was impeding air traffic controllers.

Federal Transportation Secretary Sean Duffy said the source of the strong odor was traced to a circuit board that overheated and was replaced.

The Newark Liberty was not related to a fatal accident at New York’s LaGuardia Airport on Sunday night.

In that episode, two people were killed and several others were seriously injured when an Air Canada regional jet struck a fire truck on a runway while landing, as Breitbart News reported.