Residents in Portslade were warned to stay in doors as gas cylinders exploded in a factory inferno.
Flames leapt in the air and thick black smoke could be seen for miles around.
More than 60 firefighters battled the blaze which threatened to spread to Portslade Town Hall.
The blaze became so intense and the smoke so acrid that a Sussex Police van drove through nearby streets advising residents to shut their doors and windows for safety reasons.
Neighbours poured into the streets around the Hosiden Besson electrical factory off Victoria Road, Portslade, at 11pm last night as thick smoke and the sound of exploding cylinders filled the air.
Stuart Hunt, 40, of St Albans Road, Fishersgate, said: "I thought it was a fireworks display until I looked out my window and saw the smoke."
Tony Wright, 38, went out onto the street with his partner Paula Blakeborough, in her nightclothes, to watch the drama unfold.
Mr Wright of Westbrook Way, Southwick, said: "We wondered what was going on. It was so loud it sounded like fireworks and the smell was really bad."
Wendy Lockwood, of Victoria Road, said: "My sister-in-law and brother are staying with us for a week and we heard the noise of crackling and went out in the back garden to find out what was going on. Then we saw the flames and sparks and realised something bad had happened.
"Nothing like this has ever happened down here before. It is absolutely terrible."
Becky Morris of Manor Hall Road, Portslade, said: "I heard the crackling and saw the smoke from my bedroom."
Ten fire crews from across the county, police units and ambulances were called to the scene.
Brighton and Hove city councillor Steve Collier, who lives in nearby Victoria Road, Portslade, said: "The fire was like an out-of-control firework night, very intense flames from a fair distance away, explosive sounds punching the air at irregular intervals, with sprays of showering embers."
"For a spell there was a purple glow around the fire. The smoke was thick, becoming blacker as the fire was contained."
The blaze was very close to Portslade Town Hall and there were fears it could spread as the blaze raged at it peak.
Brighton and Hove City Council said Portslade Town Hall would be closed for at least 24 hours with staff directed to King's House in Hove.
Fire investigators were today examining the the debris to find a cause for the blaze.
The road has been cordoned off to both traffic and pedestrians and the gas main in Victoria Road has been shut while the area is made safe.
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