Departure flights resumed at London's Heathrow Airport on Tuesday after they were briefly suspended following reports of a drone sighting.

"We are working with Air Traffic Control and the Met Police, and have resumed departures out of Heathrow after a short suspension," authorities at UK's busiest airport said on Twitter.

"We will continue to monitor this and apologise to anyone that were affected," it said.

Meanwhile, the Metropolitan Police said it was investigating the alleged drone sighting which led to outgoing flights being temporarily grounded for an hour.

British Transport Secretary Chris Grayling said the military was preparing to deploy the same equipment at Heathrow that was used at Gatwick in the wake of a drone scare.

"I have already spoken to both the Home Secretary and Defence Secretary and the military are preparing to deploy the equipment used at Gatwick at Heathrow quickly should it prove necessary."

London's second busiest airport, Gatwick, was severely disrupted when drones were sighted on three consecutive days in December, resulting in about 1,000 flights being cancelled or diverting and affecting 140,000 passengers.

The army deployed unidentified military technology to guard the area, reassuring the airport that it was safe enough to fly.

Heathrow and Gatwick responded by ordering military-grade anti-drone defences worth "several million pounds".

Heathrow said earlier this month it was working closely with authorities including the police and looking at relevant technology to combat the threat of drones.

UK government introduced new police powers against drones flown near airports this week.