One of the drones came within 30 feet of an aircraft, according to one pilot, whose comments prompted the decision to close Newark International as a precaution.
In a statement, the Federal Aviation Authority (FAA) explained: "At approximately 5pm, we received two reports from incoming flights into Newark that a drone was sighted at about 3,500ft above Teterboro, New Jersey.
"At that point, flights arriving into Newark were held for a short duration. Since then, and with no further drone sightings, arrivals have been resumed.
"However, we still have a ground stop in place at other airports departing for Newark until a backlog of arrivals can be cleared. We expect that to be lifted soon."
United Airlines - which uses Newark as a hub - said that despite the frustration, the disruption caused by the drones has been "minimal".
The company explained: "The impact to our operations has been minimal so far. We are working closely with the airport and the FAA to return our operations to normal as quickly as possible."