MADRID (AP) — A huge explosion Monday at a fireworks factory in northeastern Spain killed five people and seriously injured three others, police said.

The blast occurred around 2 p.m. (1200 GMT) at the Pirotecnia Zaragozana factory in the small town of Pinseque, a police spokeswoman said.

The blast sent a dense plume of white smoke into the sky that could be seen for kilometers (miles).

The injured were taken to a hospital in the nearby regional capital of Zaragoza, she said on condition of anonymity because of police regulations preventing her from being named.

Police and firefighters didn't know the cause of the blast and were prevented from trying to investigate it because fires were still raging at the site hours after the explosion and a series of smaller blasts.

Spanish national television said the blasts in the aftermath of the main explosion initially hindered a search operation for missing people.

By late afternoon, no more people were reported as missing, the spokeswoman said.

The factory was purchased in January by Etienne Lacroix Group and the French company said at the time that the plant's Spanish management team would continue running the business.

A woman who answered the phone at Etienne Lacroix said the company based near Toulouse had no immediate comment and referred inquiries to a company manager who did not immediately respond to an emailed message seeking comment.