Medical officials said at least one person was killed.
The dead person was found in the collapsed building.
A tweet by emergency services for the Catalonia region called the blast a "chemical accident" and advised residents to refrain from going outside as a preventive measure, as well as to close all windows.
Early reports suggested that 6 people had been injured in the explosion, at least one seriously, according to emergency services in Tarragona.
Multiple other videos of the aftermath of the initial blast have also appeared online, showing red and black plumes of fire and smoke rising into the sky.
Social media users posted videos of the incident. Authorities also asked people not to drive in the area and train services were suspended.
The coastal city of Tarragona, with its 800,000 residents, is located some 115 kilometers (71 miles) southwest of Barcelona. Since 2015, it has housed a 1,200-hectare chemical hub known as ChemMed which is the largest of its kind in southern Europe, AP reported.
Quim Torra, Catalonia's president since 2018, said he was monitoring the situation.
Tuesday's explosion comes just over a month after a blaze at a solvent and industrial residues recycling plant in the northeastern town of Montornes del Valles on December 11.