Mexico City: Plunged into chaos just hours after entering this world, nine babies found alive after a gas blast in a Mexican maternity hospital underwent DNA tests on Friday in a bid to reunite them with their parents.

Thursday's blast devastated the hospital on the western edge of Mexico City, sending a fireball into the air and killing a nurse and two infants. But dozens of people, including mothers and newborns, who were inside at the time survived, many cut by broken glass.

"We have nine DNA tests pending," Mexico City Mayor Miguel Angel Mancera said. "There are parents who have identified their children, but as the babies did not have bracelets on, we have to follow a protocol to identify them."

Mancera said several babies survived because their mothers sheltered them with their own bodies during the blast.

A leak in a hose from a gas truck, which was fueling the hospital's tanks, was believed to have triggered the explosion, officials said.

Many areas of Mexico City have no mains gas supply and rely on deliveries from gas trucks. Mancera said the gas truck company involved had been working in Mexico City since 2007.