The fire officer in charge at the Deptford blaze has spoken about the situation.
Station Manager Steve Graham is on the scene at the former Alex Smiles Ltd premises and said at the moment they have four engines there.
They also have two aerial ladder platforms and a volume pump on site.
He said: "At this time the focus of the operation is to contain the fire that we have in the two large units."
The fire officer said they are also testing the toxicity levels in the water.
At the height of the blaze at the Deptford plant up to 50 firefighters tackled the blaze, which could be seen for miles around.
Crews were called at around 6pm last night, were still on site this morning and are expected to be there for the rest of today.
Fire crews work through the night
Alex Smiles Ltd, fell into administration in early 2015 with the loss of about 80 jobs.
The company was created by the late Alex Smiles in the early 1970s and remained based in Wellington Lane until the turn of the century, moving to Deptford in 2002.