A massive explosion at a petrochemical plant in northeastern Spain killed one person and gravely injured at least six others Tuesday, regional authorities said. One person remains missing.

A local government spokesman for the port city of Tarragona, where the plant is located, said a preliminary investigation indicated the force of the blast killed an individual in a nearby neighborhood.

The spokesman said he had no further details. He spoke on condition of anonymity in keeping with City Hall regulations.

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The civil protection agency in the Catalonia region called the blast a "chemical accident" and warned people in parts of the city of 800,000 and in nearby towns to refrain from going outside as a precaution. Emergency services said that two of the injured were being treated for major burns.

Buch said the smoke from the resulting fire was not toxic but he also advised residents to remain inside.

Smoke rises following a major explosion at an industrial hub near the port city of Tarragona, Spain. David Oliete / AP

The blast took place on the premises of Iqoxe, according to a woman who answered the phone at the company and who quickly hung up the phone without giving her name.

According to the company's website, Iqoxe is Spain's sole producer of ethylene oxide, a chemical compound used for making detergents, solvents and other products, as well as ethylene glycol, one of the main raw materials in the production of plastics.

Local residents posted videos showing the aftermath of the blast, with flames and a big column of black smoke emerging from an area dotted with large industrial tanks.

Fire departments sent 24 brigades to the area, the regional emergency service said.

Some local residents told Tarragona Radio that the blast could be heard from miles away.

Tarragona is located 71 miles southwest of Barcelona, the regional capital of Spain's Catalonia region.

Since 2015, the city has housed a 2,965-acre "chemical hub," ChemMed, that was described as the largest of its kind in southern Europe.

The government said Prime Minister Pedro Sánchez had been in contact with the regional president of Catalonia, Quim Torra, to inquire about the blast and offer any help needed.

Tuesday's explosion comes just over a month after a December 11 blaze at a solvent and industrial residues recycling plant in the northeastern town of Montornes del Valles. After that blast, which caused no casualties, authorities had to cordon off an area of some 550 yards in radius around the plant.