The blaze, in the coastal city of Vilanova i la Geltru just south of Barcelona, took hold of a building storing pool cleaning products, the regional fire service said.

“If you are in the zone that is affected do not leave your home or your place of work,” the Civil Protection service said on social media.

The at-risk area stretched across five municipalities from Vilanova i la Geltru to the village of Calafell, near Tarragona.

“No casualties” had been reported, the fire service said on X, adding that a large number of units deployed to the scene had brought the fire under control.

It said it was “monitoring the column (of gas) caused by the blaze for changes and for its toxic levels”.

“It is very difficult for chlorine to catch fire but when it does so it is very hard to put it out,” the owner of the industrial property, Jorge Vinuales Alonso, told local radio station Rac1.

He said the cause of the fire might have been a lithium battery.