A chemical accident at a factory in Spain on Thursday injured three people and cloaked large swathes of the region in an orange chemical cloud, forcing over 60,000 people to stay indoors before it disappeared.

The "explosion or chemical reaction" happened when products being "loaded or unloaded" at a factory owned by Simar at an industrial zone in the northeastern town of Igualda became mixed, a spokeswoman for Catalonia's firefighters said.

Local officials ordered around 64,500 people in Igualda, about 70 kilometres (40 miles) northwest of Barcelona, and four other towns to remain indoors with their windows shut.

About 60 firefighters wearing protective clothing spread out across the region to order local residents to return home.

The general warning was lifted about an hour later but maintained for another three hours for pregnant women, children, the elderly and those with respiratory problems.

A huge bright orange cloud was caught on camera by local residents who distributed their photos and videos on social media sites.

The cloud may have been caused by a reaction between nitric acid, which is corrosive and toxic, and ferric chloride and another chemical which still has not been identified, the regional Catalan government said in a statement.

Two employees who were transporting chemicals were lightly burned and a worker at the Simar plant was also injured, the statement added.