The fire started at the Thor Chemicals premises in Ramsgate Road in Margate on Wednesday morning.
Six fire crews were sent to douse the flames, which have now been put out. The factory was evacuated with no reports of any casualties.
Residents had been advised to stay indoors but police have now said there is no danger. A 300m (984ft) cordon around the site has also been lifted.
"I was sitting in my dining room having a cup of tea when suddenly the whole place shook"
Kent Police said: "The advice was given as a precaution after an explosion was reported at the Thor Chemicals site in Ramsgate Road at 1005 GMT.
"Kent Fire and Rescue Services has confirmed the fire has now been put out."
John Cook, 82, who lives in Ramsgate Road said he felt his house shake when the fire broke out.
He said: "I was sitting in my dining room having a cup of tea when suddenly the whole place shook.
Serious congestion
"I went into the garden and looked over towards the warehouse where big thick black plumes of smoke rose for about 15 minutes."
Thirty firefighters were sent to tackle the blaze.
Police had closed roads near the factory but they have now all been reopened.
Thor Group Ltd is a multinational company that produces a range of chemicals used in items such as hair and skin products and flame retardant products.
Its headquarters are in Margate and its main manufacturing plant and technical facility is in Germany.
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