At least 21 people have been killed in a fire that broke out in a factory in eastern Pakistan after sparks from a generator hit chemicals used to make shoes, police said.

Senior police officer Multan Khan said six people were also injured in the blaze at the factory in Lahore.

The fire broke out when people in the building were trying to start their generator after the electricity went out. Sparks from the generator made contact with the chemicals, igniting the blaze.

Pakistan faces widespread blackouts, and many people use generators to provide electricity for their houses or to run businesses.

Pakistani television showed pictures of what appeared to be a three-story building with flames leaping from the top-floor windows and smoke billowing into the night sky.

Pakistani Prime Minister Raja Pervaiz Ashraf expressed his shock and grief over the deaths.

Many people in Lahore have set up shoe factories at homes and in residential areas. Many of the factories are ill-equipped and often lack modern fire safety equipment such as fire extinguishers or sprinklers.