An explosion at a chemical plant owned by French pharmaceutical giant Sanofi-Aventis in the southern Italian town of Brindisi killed one and injured four with burns, the company said.

"The plant's managers are at the disposal of the competent authorities to ascertain the causes" of the blast, it said in a statement.

The employee who died worked for a local company as well as three of the injured, while the fourth injured worker is a Sanofi-Aventis employee, the ANSA news agency reported.

The explosion happened during a welding operation on a tank containing chloroform water, which is used as a perservative for liquid pharmaceuticals, according to Brindisi authorities.

The plant, employing about 200 people, produces active ingredients used mostly in the production of antibiotics.