"There was an explosion with several people injured for as-yet undetermined reasons at around 11:30 at BASF Ludwigshafen," the company said in a press release.
Speaking at a press conference on Monday afternoon, a city official confirmed that at least one person had died in the blast, while six others had been injured, and a further six were still missing.
"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.
BASF has warned residents to remain indoors, though a company official later said there was no risk to locals.
"We have not been able to establish any danger to the population," BASF executive Uwe Liebelt said at a press conference, after residents were ordered to stay inside and shut their windows and doors.
According to the Frankfurter Allgemeine Zeitung, the explosion was set off during repair works on a pipeline, which is used to transport products between ships and the factory.
The city of Ludwighshafen tweeted that several residents had called in complaining of breathing problems.
In neighbouring Mannheim, local authorities also warned that a dangerous cloud of chemicals could also spread across the city, instructing people to keep doors and windows closed.
Ludwigshafen is located around 80 kilometres southwest of Frankfurt.
The Landeshafen Nord site where the explosion took place is a harbour used for the transportation of combustible fluids and liquefied gases.
On its website, BASF describes the site as a "very important for BASF's supply of raw materials", where more than 2.6 million tonnes are handled each year.
The goods are unloaded from ships into the production plants via a system of pipelines.
BASF is a global giant in the chemical industry, employing over 110,000 employees worldwide and with sales of more than €70 billion last year.
Emergency services attempt to quell the flames. Photo: DPA
BASF was also grappling with a second, smaller incident at its nearby Lampertheim plant where four people were injured in a gas explosion and had to be taken to hospital, DPA news agency reported.
That incident is also still being investigated.
In the company's deadliest incident to date, nearly 600 people were killed in 1921 in an explosion at an ammonia plant near Ludwigshafen.
In 1948, 200 people died and more than 3,800 were injured when a rail tanker exploded, also at the Ludwigshafen complex.