A gas truck explosion decimated large parts of a maternity hospital on the western edge of Mexico City on Thursday, killing at least seven people including three children, and leaving many others missing, officials said.

Several babies were found alive under the rubble but dozens of people were unaccounted for, as scores of rescue workers continued to scour through the concrete and twisted metal in search of survivors.

People seeking information on family members gathered around police lines that were set up to keep bystanders away from the chaotic scene.

“I am so worried about my sister, she’s supposed to have given birth, we brought her in yesterday,” said Monserrat Garduno, a 32-year-old nurse. “They won’t let us pass, I want to know how she is.”

Mexico City Mayor Miguel Angel Mancera said dozens of women and children were evacuated from the site, some with cuts from broken glass.

More ambulances waited at the scene to treat survivors pulled from the wreckage. Around 100 people were in the hospital at the time of the explosion, according to a city official. About 60 have been accounted for.

Ana Maria Sanchez, 47, wept as she stood in the crowd beyond the police lines, waiting to find out about her sister who worked in the hospital’s administrative area. She said her calls to her sister’s phone went straight to voice mail.

“I haven’t heard anything about her, they have us just standing here,” she said.

Some of the injured were evacuated by helicopter, and aerial footage showed firefighters scrambling over the skeletal wreckage of the building.

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

Rescue workers are seen at the site of an explosion at a maternity hospital in Mexico City