At around 6pm, the airport tweeted: "We are responding to a drone sighting at Heathrow and are working closely with the Met Police to prevent any threat to operational safety. As a precautionary measure, we have stopped departures while we investigate. We apologise to passengers for any inconvenience this may cause."
This comes after dozens of sightings of illegal drone activity at the site between 19 and 21 December caused 140,000 passengers' flights to be cancelled.
The culprits responsible for the incident still have not been found. Click here for the full story.
Flights were resumed about an hour after the first sighting. Police continue to investigate the incident.