Five migrant labourers were killed and several were injured in a blast in a firecracker manufacturing and packaging unit near a village in Punjab's Sri Muktsar Sahib district on Friday, police said.

The incident occurred in the two-storey factory unit located on the Singhawali-Kotli road in Sri Muktsar Sahib, Lambi's Deputy Superintendent of Police, Jaspal Singh, said over the phone. 

The cause behind the blast is under investigation, the DSP said.