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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Rain will arrive in the southwest of the region early this evening, before spreading to other areas.
A largely dry night is expected in northern areas, patchy rain in south.