KOLKATA, India (AP) — A fire broke out at an illegal six-story plastics market in the Indian city of Kolkata early Wednesday morning, killing at least 18 people, police said.

The blaze, which started before 4 a.m., was likely caused by a short circuit, said West Bengal fire minister Javed Khan. The fire was under control by mid-morning, he said, but toxic gases being released by the blaze was hampering rescue efforts.

A police official, speaking on condition of anonymity because he was not authorized to speak to the media, said at least 18 people had died. He said police were looking for the owner of the building, which was filled with dozens of small shops selling various plastic products.

At least eight people were hospitalized in critical condition and the death toll was expected to rise, Khan said.

He called the scene of the fire “an illegal, unauthorized market.”