The fire service and ambulance service are on the scene of what is understood to be a building fire in London Road in Hassocks.
Several emergency service vehicles attended the blaze including six fire crews at the peak.
The fire service confirmed it was called at 1.28pm to a derelict barn fire at London Road.
A spokeswoman added: “On arrival the building was well alight and at its peak we had six crews in attendance. However, the incident is beginning to be scaled down.
“All people are accounted for.”
An ambulance service spokesman confirmed crews attended the incident.
He added: “Ambulance crews, including our Hazardous Area Response Team, are currently at the scene.”
Traffic is reported to be coping well despite the incident, according to the AA.
Sussex Police have been approached for comment.
1.
2.
The scene of the incident.
3.
4.