It is the latest in a series of protests carried out over the past two months at the entrance to Third Energy's site in Kirby Misperton, near Malton.
North Yorkshire Police said two pairs of people are currently lying in the middle of the carriageway at different points on Habton Road.
The protesters laid down in the road at about 6.45am today, forcing its closure yet again.
Officers are working to remove them so that access can be restored as soon as possible, with the force saying a number of local businesses have already been affected by the blockage.
Superintendent Alisdair Dey, of North Yorkshire Police, said: "Habton Road is blocked at both ends due to the actions of these four people. This has caused substantial disruption to the local community, including local businesses and people on their way to work and school.
"We understand that protest activity connected to hydraulic fracturing is now having a significant impact on the local community, and we are doing all we can to reduce that impact."
Residents and businesses are urged to use alternative routes for their journeys until the situation is resolved.
Local diversions are in place in the meantime.