50 firefighters are tackling a blaze at G&P Batteries on Willenhall Road, Walsall.
ITV News Central has been told by eyewitnesses that a number of loud explosions could be heard at the plant.
It is the second time this year a fire has broken out at the factory - the previous one on 14 January saw 60 firefighters in attendance.
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Very cold tonight. Mainly dry and bright in the day.
Staying very cold.
A whistle-blower told ITV News some school buses were on the road without a valid MOT.