A fire at a shack in an impoverished Mexico City neighbourhood Friday killed seven children, authorities said. It was not known what caused the pre-dawn blaze at the sheet metal-and-cardboard shack in the densely populated neighbourhood of Iztapalapa, on the sprawling capital's east side.

The fire was similar to another less than a month ago that was caused by a gas leak, said the top city official for the area, Clara Brugada. "We're going to investigate (what caused the fire), but we will have to launch a campaign on how to use gas heaters safely in the winter," she said.