"There was an explosion with several people injured for as-yet undetermined reasons at around 11:30 (0930 GMT) at BASF Ludwigshafen," it said in a press release.
"Emergency services from the whole region are on the scene to prevent the fire spreading to other parts of the plant," Ludwigshafen city authorities said in a statement.
The company said local residents should remain inside and shut doors and windows.
"We are still investigating the precise cause. The relevant authorities have been informed," BASF said.
Ludwigshafen is located around 80 kilometres (50 miles) southwest of Frankfurt.
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