British climate-change activists said they would fly toy drones at London's Heathrow airport from September 13, a step that is likely to ground all flights, to put pressure on the government to take tougher steps to reduce greenhouse gases.

The "Heathrow Pause" group said it would fly toy drones within the restricted zone but outside the flight paths of the airport, a step the group said would force the airport to ground flights.

"This is a symbolic action, using a legal loophole and participants' self-sacrifice to draw attention to the most serious and urgent crisis humanity has ever faced," the group said.

"The government's inaction on climate change, and the looming catastrophe of airport expansion, gives us no choice, and compels us to act," the group said.

Heathrow is Europe's largest airport.

A spokeswoman for Heathrow declined immediate comment.

Heathrow Pause said it would fly drones at no higher than head level and give the airport one hour's advance notice.