A large toxic cloud spread spread over Catalonia, Spain on Thursday, and residents of several small towns near Barcelona were told to stay indoors.

Reuters reported the thick orange cloud resulted from an explosion at a chemical plant in northern Spain that also injured three people. The incident occurred in Igualada, some 40 miles from the Catalan capital, according to pictures and television footage.

The blast was apparently caused by two chemicals coming into contact during delivery to the plant, owned by Spanish company Simar, the regional government of Catalonia said in a statement.

Police said the explosion occurred at 9:45 a.m. local time, The Independent detailed. By 11 a.m., the confinement order was partially lifted, Reuters added.

Firefighters and Civil Defense ordered 66,000 residents in the Catalan towns of Igualada, Jorba, Òdena, Sant Martí de Tous, Santa Margarida de Montbuí and Vilanova del Camí to stay inside and close windows and doors, The Independent said.

Students from a local school who were in nearby woods to celebrate a carnival witnessed the explosion, but none of the youngsters were injured.

A school in Òdena informed parents that their children needed to remain on the premises due to the confinement order, La Vanguardia reported.

"Your sons and your daughters have been confined within the facility and cannot go outside. We ask for calm because the best that can be done is to remain inside the building," school officials explained. "We ask you not to approach. The door cannot be opened as no air may enter (the building)," they added.

Several rail lines were interrupted due to the incident, and authorities closed two exit ramps of the A-2 highway, according to the Barcelona newspaper.

The European 112 emergency line received almost 400 calls concerning the incident, and authorities asked residents not to call the hotline if they merely required information. Catalan Civil Defense said their 012 non-emergency number was available for that purpose.

The cloud is expected to remain above the affected area for the time being, and how long it will take for it to disperse will depend on meteorological conditions, La Vanguardia reported.