Around 50 firefighters are battling a fire at a Croydon tyre shredding plant.
Half of the two-storey building, on Purley Way, is alight with surrounding roads closed to traffic amid fears containers on site could explode.
An exclusion zone is in place around the site after firefighters were called at around 1.15am.
Station manager Lisa Hicks said: "There is a partial collapse of the building which is 60 metres by 40 metres.
"It contains a number of tyres and thick black smoke is going across the nearby A23.
"The A23 Purley Way is closed in both directions between Wadden Way and Edgehill Road. Cylinders are also believed to be involved.
"An exclusion zone has been set up as some cylinders can explode when exposed to heat. Three people left the building before the Brigade arrived."
The cause of the blaze is not yet known.
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