A fire broke out in two factories in Narela here following a cylinder blast on Tuesday morning, a Delhi Fire Service official said.
One of the factories is manufactures shoes.
A call was received about the first blaze at 4.52 am and 32 fire tenders were rushed to the spot.
Soon after reports were received about the second blaze.
Three firemen received minor injuries fighting the fires and returned to work after first-aid.
"The firefighting is underway at both the locations and it is believed that no one was trapped inside the building, an official said.