Kolkata: At least five people were injured in a blast at a firecracker unit in West Bengal's South 24 Parganas district on Thursday, police said.The explosion occurred at the factory in the Champahati area around noon, following which a fire broke out at the unit, a senior officer said.Locals found the factory engulfed in flames, with thick smoke billowing from there, he said.Also read: Kolkata hotel fire: 9 dead, several injured in massive blaze at Mirza Ghalib Street; CM orders SIT probe"Five people have been injured in the blast. A fire brigade team reached the spot," the officer said.A probe is underway to "ascertain the exact cause of the blast and to check whether the unit had the requisite licence and followed safety norms", he said.