A gas blast killed seven people at a maternity and children's hospital in Mexico City on Thursday.

According to The Associated Press, Mexico City's civil defense agency spokeswoman Claudia Dominguez said she expected the death toll to rise from the AP's reported four deaths. A more recent report from USA Today reports seven deaths.

Mayor Miguel Angel Mancera said at least 54 people were injured at The Cuajimalpa Maternal Hospital, 22 of them being children. Most of the injuries were caused by flying gas and said to be minor. About eight serious injuries were reported.

Rescuers continued digging through the rubble as more people were expected to be underneath the hospital since most of it collapsed. The heaviest damage was said to be near the hospital's loading dock.

Mancera said the blast may have been caused by a leak in the hose carrying gas from the tank truck to the hospital. According to Mancera, fire continued burning because firefighters recommended that they allow the truck's remaining gas to burn off as there was no risk of another explosion.

The explosion sent a blanket of smoke over the western edge of Mexico City, CNN reports. Witnesses say they saw everything catch on fire as a result of the explosion.

According to USA Today, Ismael Garcia, a resident that lives a block from the hospital, heard the gas tank truck explode and rushed to the hospital with a few other citizens to help rescue the babies from the nursery.

"Fortunately, we were able to get eight babies out," he said.

Injured infants were taken to a nearby hospital.

Four children are dead as a result of the explosion, CNN reported. There is fear that more children are trapped underneath the debris of the hospital.

The Red Cross provided 23 ambulances and more than 40 rescuers to help with saving people.

Mancera added it was a controlled fire designed to burn off the leaking gas.