The suspension of takeoffs from Heathrow, one of the world's busiest airports, was announced shortly before 6 p.m. on Tuesday, a move the airport said was made as a safety precaution.
Those measures came in response to earlier drone sightings that shut down Gatwick airport in the days before Christmas, causing disruption for more than 120,000 passengers.
Heathrow wants to accommodate an extra 25,000 flights per year ahead of the planned opening of a new runway at the airport.
Frustrated passengers are taking to social media to express their frustration with the Heathrow drone chaos - with one suggesting "it was probably a plastic bag blowing in the wind".
About an hour later, Gatwick resumed operations, saying "The military measures we have in place at the airport have provided us with reassurance necessary to re-open our airfield".
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Arriving planes, however, are continuing to land at Heathrow.
"As a precautionary measure, Heathrow Airport has stopped departures and officers based at Heathrow are now investigating the reports with colleagues from Heathrow Airport", they said.
The Metropolitan Police is investigating reports about the sighting of a drone near London's Heathrow Airport.
Heathrow and Gatwick recently also spent millions of pounds on military-grade anti-drone equipment.
On Tuesday, the Government announced a package of measures created to give police extra powers to combat drones. The government will also extend drone exclusion zones around airports.
Ministers announced that from 30 November operators of drones weighing between 250g and 20kg will be required to register and take an online drone pilot competency test.