Four fire engines and two police cars have been called to an address in Park Way, Hastings.
A spokesman for the fire service said crews were called at 3.52pm and remain on scene.
There are not thought to be any injuries.
East Sussex Fire said: “Four appliances, including the aerial ladder platform, sent to a property in Park Way, Hastings, at 3.52pm this afternoon where they are currently tackling a fire.
“Six firefighters wearing breathing apparatus are using two hose reel jets to get the fire under control.
“Everyone accounted for and the incident is still on-going.”