Firefighters who are still trying to contain a fire at a chemical plant in the Ural city of Perm prevented an explosion on Tuesday, an emergencies service spokesman said.

A fire broke out early on Tuesday at a plant owned by Russia's largest petrochemicals holding, Sibur, and rapidly spread over 300 square meters.

"There are 30 fire engines and 108 firefighters currently working at the scene. No casualties have been reported," Valery Tiunov told RIA Novosti.

The company's spokeswoman confirmed the reports.

"Firemen are still struggling to bring the blaze under control. The cause is yet unknown. An official comment will be issued later in the day," she said.