Construction work has started on Terminal Five
A road has been closed in west London because of a demonstration by what are believed to be campaigners against airport expansion.
Two protesters are hanging by ropes from a temporary construction bridge on the A3044 near Heathrow Airport, Scotland Yard said.
Three others are obstructing the bridge, which is used by site traffic.
The demonstration, which is thought to be over the building of Terminal Five at the airport, is causing long delays and motorists are being advised to avoid the area.
In October campaigners occupied a crane on the construction site for several days.