Watch Malcolm Shaw's report:
Firefighters with specially trained sniffer dogs were searching for any injured or trapped people after 500 tons of flint stone collapsed on buildings when part of historic Lewes Castle's walls gave way and toppled to the ground below.
The castle, built in the 11th century, is one of the most historic landmarks along the South Coast and stands proudly over the town of Lewes.
Fire crews called in the sniffer dogs and requested a drone to fly over the rubble which crashed down on buildings including the Old Coach House which is privately owned in the town's Castle Ditch Lane.
Footage: Eddie Mitchell
Paramedics in several ambulances along with police were also called to the castle after the large section of flint wall collapsed and crashed to the ground.
It was not immediately known whether anyone had been standing under the castle walls when the collapse happened and a full scale search operation was mounted.
Lewes Castle, built in 1068 by William de Warenne, the 1st Earl of Surrey, is a popular tourist attraction.
The Norman castle occupies a commanding position guarding the gasp in the South Downs cut by the River Ouse and stands on a man-made mount just north of Lewes High Street. It was constructed of flint blocks and local limestone.