The emission appears to have occurred in connection with the flames reaching a storage building for pool cleaning products in Vilanova i la Geltrú.
"If you are within the affected zone, you should not leave your home or workplace", the civil defense authority wrote on social media in the morning.
Early in the afternoon, Catalonia's Minister of the Interior Nuria Parlon announced that the lockdown had been lifted. However, certain harmful particles may remain in the air, so children and people with health problems are advised to continue staying indoors.
Several roads and train stations in the area were closed to prevent people from approaching the risk area.
There are no reports of anyone being injured in connection with the fire or emission.
