Recordings of the conversation between air traffic control in San Diego and a United Airlines flight reveal the pilot believed his Boeing 737 could have made contact with a small airborne device.

The incident happened around 8.30am (1630 GMT), 90 minutes after the plane took off from San Francisco, flying at an altitude of around 3,000 feet (900 meters).

“It was so small I couldn’t tell,” the pilot told controllers who had asked for more details about the possible drone strike.

“It was red…it was shiny.”

A few minutes earlier, the pilot had radioed the control tower to ask if other aviators had reported anything unusual in the skies.

“I believe I just saw like a red small object…about 1,000 feet below us to our right,” the pilot said.

A spokesman for United Airlines confirmed the potential drone sighting, but said it had caused no damage and there were no injuries among the 48 passengers and six crew on board.

“United flight 1980 reported a potential drone prior to arriving in San Diego,” a statement from the airlines said.

“The flight landed safely, and customers deplaned normally at the gate. Our maintenance team found no damage after thoroughly inspecting the aircraft.”

Federal Aviation Authority rules ban the use of drones above 400 feet unless specifically authorised, and operators must avoid restricted airspace, including that around airports.