NEW DELHI (Reuters) - An explosion at a firecracker factory in India’s northern state of Uttar Pradesh killed eight people and injured three on Friday, police said.

“The roof was blown away due to the impact of the explosion. The reason is not immediately clear,” said Surendra Singh, a police official in Badaun district.

Millions of fireworks will be set off during the Hindu festival of Diwali next month and shops are stocking up on supplies.

India’s Supreme Court said this week only “environmentally safe” fireworks would be allowed, to limit the high pollution across the country.